Rules As Written
The basic answer is no. The Oversize Weapon Master allows you to do it, it does not change the characteristics of the weapon.
Ideas
There are really two types of Spears, 1 handed which would be throw and used with a shield and 2 handed which could not.
The +1 Parry on a Spear probably comes from abstracting it reach and forcing your opposed to be further away. I can't see how using it with one handed changes this. If this is a normal one handed small spear then there should already be no reach bonus as it is shorter.
Forgetting about the fact that Great Swords is an incorrect naming (and the weight is off too) then the idea of the -1 is because of the over balancing from using this type of sword. I can't see why using it one handed would negative this, unless you where also well over the strength required. As you need a d10 strength normally you could house rule that some one with d12+2 strength does not have the penalty.
First off, it's worth mentioning that Deadlands: Hell on Earth Reloaded is not intended to be combined with Deadlands Reloaded, so you are in homebrew territory here. That said, this is a question that is probably relevant to Deadlands Reloaded as well.
Misunderstandings
There are several misunderstandings here that we first need to clarify:
Chi Mastery gives two powers with unlinked skills.
Unlike Arcane Background (Super Powers) in the core rules, you get two powers by taking Deadlands Reloaded's Arcane Background (Chi Mastery). As with Arcane Background (Super Powers), you cast each power with a unique skill (e.g. the "Bolt" skill to cast bolt), which can be used untrained. But unlike Arcane Background (Super Powers), each power skill is linked to Spirit, rather than having no linked attribute.
To get two powers to d8 that's one advance for the base ability then two each for the power skills, for a total of five advances.
I'm not sure where you got this from (I presume that "one advance for the base ability" refers to buying a new skill at a d4), but here is how the advances work:
Advance 1: Buy skill A (e.g. Bolt) at d4
Advance 2: Buy skill B (e.g. Deflection) at d4
Advance 3: Increase skills A and B to d6
Advance 4: Increase skills A and B to d8
This is not much different than other Arcane Backgrounds, like Arcane Background (Spellcasting):
Advance 1: Buy arcane skill (e.g. Spellcasting) at d4
Advance 2: Increase arcane skill to d6 and another skill one step
Advance 3: Increase arcane skill to d8 and another skill one step
One commonly overlooked rule is that you can't increase a the same skill twice for an Advance. So it only takes one more Advance compared to other Arcane Backgrounds.
Note that it is cheaper to buy Chi Mastery skills at character creation, as raising a skill to a d4 only costs one skill point then (an Advance is equivalent to two skill points, but raising to a d4 costs a whole Advance). It's a pretty common houserule to drop the "whole Advance" rule and just have it work like character creation.
It does get credit for 20 starting power points, equal to two advances.
I don't think it's good to compare 20 Power Points to "two advances". Yes, compared to Arcane Backgrounds that have 10 Power Points, it's like taking the Power Points Edge twice, but this is to offset the downsides of this.
should I hold out for, say, a Templar or even just a Miracles background, and get more long term potential (along with STUPID good perks or a lot more flexibility)
Yes, the Templar Edges are very powerful. However, they all require either spending a Benny (a limited resource), or they are only useful in specific situations, such as fighting supernatural evil (not just the regular kind of evil that humans can create).
The other advantages of Chi Mastery
Aside from 20 Power Points, there are several advantages to Chi Mastery over other Arcane Backgrounds:
- You can multi-action powers: Since you can't use the same skill twice in a round without something saying you can, a martial artist can cast two powers in a round. A Huckster or a Syker can't cast both Bolt and Deflection in the same round (they can only use Spellcasting or Psionics once), but a Martial Artist can since they are separate skills.
- There is no penalty for failing to cast a power: Whenever they fail to cast, Hucksters suffer from Backlash and Templars take a level of Fatigue. Martial Artists suffer absolutely no consequences if they fail.
- Virtually all their powers have no visible effect: You can instantly tell a Syker by their shaved head and Hucksters have to worry about people spotting magic cards. Martial Artists have neither problem, so they are easy to underestimate and perfect for stealth missions. Only Deadlands Reloaded's Arcane Background (Miracles) has this advantage.
The Superior Kung Fu Edge
These are usually pretty average Edges in my opinion, generally equivalent to combat Edges. You called out Wing Chun in particular. It's just like Improved Frenzy (which, being an Improved Edge takes two Advances to get), but being a single Edge only takes one Advance. In my opinion, this makes it probably the best of the Superior Kung Fu Edges. Also if you manage to get both of them, they stack, so you can make three attacks in one round.
Should I go for it?
That depends on what you're looking for:
- I want to attack a whole bunch of times: Absolutely yes. You said you'd get Quickness, which in Savage Worlds Deluxe says that you get a whole extra turn on your action card. So you double all your attacks and get twice as much movement.* For one Edge, you can get Superior Kung Fu: Wing Chu, allowing you to have four attacks each round. If you go for Improved Frenzy, you get six. Heck, go for Two-Fisted and Ambidextrous and get eight attacks per round at no penalty. No other Arcane Background can even come close to that.
- I want to attack at both ranged and melee: Yes. They are one of only two Arcane Backgrounds that are conceptually designed to fight in melee (the other being Hell on Earth's Templars), but Templars do not have access to ranged powers such as Bolt, which the Martial Artists do.
- I want to avoid backlash: Yes. If you've gotten hurt too many times by a Syker's brainburn or a Mad Scientist's exploding devices, you'll be perfectly safe with this since there is no backlash.
- I want to be able to hide my ability: Yes. They have no bodily alteration (Syker), no gear (Junker), no telltale insignia (Templars), and no visible effect to their power (Doomsayer). The only other Arcane Background that can do this is Deadlands Reloaded's Arcane Background (Miracles).
- I want lots of powers and be able to easily cast them: No. These powers are expensive, but they are powerful and reliable. The tradeoff is that you are a master of few things.
- I want lots of Edges specific to my Arcane Background: No. Martial Artists typically either improve their power skills or take more general combat Edges. They may take Superior Kung Fu, but I generally see that only being taken once.
- I want to be able to quickly make my character more powerful: No. Martial Artists require a lot more Advances to power up, especially if not happening during character creation. Other Arcane Backgrounds become much more powerful more quickly than they do, but once they do get up there, they may become more powerful.
Personally, I think that Arcane Background (Chi Mastery) is an underrated Arcane Background. There are definitely downsides in terms of breadth of powers and the fact that they take more Advances to get going, but they have a lot of advantages that no other Arcane Background has.
* For reasons that will forever baffle me, the already powerful Quickness in Savage Worlds Explorer's Edition was made even more powerful in Savage Worlds Deluxe by being changed from "an extra action" to "a whole extra turn".
Best Answer
No, you cannot activate more than one Power per turn. Activating a Power is seen as a single generic action, and as you cannot use the same action twice in a turn, you cannot activate two Powers in the same turn.
See here for official confirmation of this.
However, there is nothing stopping you activating Smite on one turn and then Deflection the next, maintaining both so that you have both effects ongoing and active.
EDIT (From Sitting Duck's answer): The Core Book Super Power AB is the exception, as each power uses a separate skill. In that case, you can activate multiple powers on the same turn while taking a standard MAP.