You've made two key changes:
- Allowing multiple combat half-actions per round
- allowing movement to be replaced by a non-movement half-action
The primary factors I see are:
- increase in Psyker offensive capability (Most of their offense is more powerful than their allowed weapons; it gets worse under RT or DW, due to a different psychic system)
- decreased access to defenses¹
- decreased emphasis on movement²
- increased emphasis on non-action defense (IE, cover)³
- breaks the equipment bonuses
- decreases incentives to use burst and full-auto autofire modes
- cybernetics and talents with extra half-actions become devalued⁴
- initiative becomes more important⁵
- Ganging up becomes less essential⁶
¹: Since one gets very few defenses per turn, this change of yours makes them less valuable, by allowing them to be overwhelmed faster.
²: The current system makes movement a valuable and essentially irreplaceable part of the round; take it or not, it's lost if unused or unusable. It's not terribly realistic, but is very cinematic. And DH, RT, and DW are all intended to be very cinematic in tone.
³: At present, especially for melee, active defenses (dodge and parry) are quite valuable; cover is less so, but not enough to render it useless. When one allows replaceing movement with a second attack, cover suddenly becomes MUCH more attractive, as it's an assured penalty to be hit, instead of a roll by the defender... but it also reduces drama.
⁴: At present, the only way to get a second attack is expensive talents and/or cyberware with inexpensive talents. If a character can just hole up in cover and double shoot, these talents are far less valuable, making the Assassin and Guardsman's additional combat actions less useful.
⁵: Further, by allowing the etra attacks, you can run a target out of actions sooner, as well, so initiative becomes more important to prevent having actions drained in defenses.
⁶: Ganging up is the great equalizer in RT and DH combats; it's how one overwhelms defenses. Given that every character can defend once for free, and once by aborting, if you can attack twice, you've just eaten both defenses this round, meaning you only need one attack from a buddy to get through. The norm is that you need two buddies to negate the defenses, or one buddy with a multiple attack talent.
It sounds like you made these changes with rank 1-2 characters... it's going to be more profoundly off-norm or higher rank characters, as normal slow growth of actions is made to feel even slower by providing far less of a bonus over not having them.
I have been playing Warhammer 40k for over a decade but am not a complete authority.
Yes, a Space Marine can remove his armour according to the Deathwatch core rulebook.
The Deathwatch core rulebook's armour section explains that it takes around 30 minutes to remove or put on power armour with 3 chapter serfs (slaves). In an emergency it can be done in 10 minutes with one serf, but no less than that, as the proper rites must be observed.
I ran a Deathwatch game on a ship where they were not in their armour and had to either put it on or fight without it - very fun and lots of RP opportunities.
In the third Grey Knights novel, the main character is captured by Chaos and made to fight on an arena world. His armour is taken and the book deals with him adapting to not having it.
Do note that when he gets it back near the end of the book, he carries it around, refusing to wear it until it can be purified by the tech-adepts. When he is forced to wear the storm bolter gauntlet it burns his skin.
Space Marines are trained to maintain a state of readiness so would remain in their armour at all times unless there was a point to removing it such as repair.
Space Marines have many enhancements such as extra organs and equipment built into their armour to deal with anything not related to killing the emperor's enemies, such as cleaning, eating or sleeping. They can do their activities in armour, they just don't have to.
As an aside: Space Marines don't have sex - they're eunuchs. Being genetically engineered to kill, genitals aren't necessary.
TLDR:
Yes armour can be removed, check deathwatch core rulebook.
Armour is taken with weapons when captured but is very difficult to get back on in this situation.
Best Answer
Yes they can
Civilians can own and use suits of Power Armor.
However, note that only Space Marines are genetically enhanced with something called Black Carapace (not related to regular "carapace armor") that allows them to interface with their Power Armor in their unique, second-skin like way. All others (including Adeptus Sororitas and the Inquisition, although they are far from "civilians") use Power Armor as normal enhanced armor. It's still impressive, but only the Space Marines profit from the full potential.
And they might
Power Armor is hugely expensive, not available for private buyers on the regular market and will surely attract attention from people whose attention normally ends in guilty and innocents dying all the same. The Inquisition and rich Rogue Traders might be able to get hold of suits, but this is nothing that a gang of rich kids might get for their 18th birthday. Well, actually, it just might be if you go back far enough in canon. The Spyre Hunters, a gang of rich kids from the upper class did just that in the game Necromunda, where gangs fought over territory in the underhive.
And then...
However, not all "Power Armor" looks like the iconic Space Marine Power Armor Mark I to X. There is Imperial Power Armor, Ex-Imperial (aka Chaos) Power Armor, Tau power armor and probably some other variants. It goes without saying that anyone owning a non-Imperial Power Armor better be having proof they killed the previous owner and are keeping it as a trophy.