[RPG] How to calculate the reduced costs of a Kineticist’s kinetic blasts with infusions

There's one big thing you're missing about Kinetic Fist. It's not extra. It's total.

You deal an additional 1d6 points of damage per 3 dice of your kinetic blast’s damage (minimum 1d6), and this damage is of the same type as your kinetic blast’s damage. This extra damage ignores spell resistance and doesn’t apply any modifiers to your kinetic blast’s damage, such as your Constitution modifier.

So at level 15, you've got as you've said a composite blast that deals 16d6+stuff damage. That means that each hit with the Kinetic Fist infusion deals +5d6 damage. There is no additional damage from Constitution and none off of the composite blast's normal base damage. Powerful Fist will up it a die step or two.

The Elemental Ascetic's flurry scales like the monk's, so you've got the ability to make three additional attacks on a full attack (technically speaking, they don't get four bonus attacks at level 16, it's just at 1/8/15. Iteratives do push it to seven though, so that's a minor nitpick).

Your damage per attack should 1d3 (base unarmed damage) + 5d# (kinetic fist) + 3 (Strength modifier) + potential amulet of mighty fists enhancement bonus + other bonuses.

Because the Elemental Flurry class feature gives you full BAB for the attacks, you've got six attacks. At level 16, you'd have seven attacks. This gives you a total of these, assuming every attack hits (which is not guaranteed, because of the massive iterative penalties):

Four Attacks

• Base die 1d6 (no Powerful Fist): 88 average (36 min, 144 max)
• Base die 1d8 (1 burn Powerful Fist): 108 average (36 min, 184 max)
• Base die 1d10 (2 burn Powerful Fist): 128 average (36 min, 224 max)
• Base die 1d12 (3 burn Powerful Fist): 148 average (36 min, 264 max)

Six Attacks

• Base die 1d6 (no Powerful Fist): 126 average (48 min, 210 max)
• Base die 1d8 (1 burn Powerful Fist): 156 average (48 min, 270 max)
• Base die 1d10 (2 burn Powerful Fist): 186 average (48 min, 330 max)
• Base die 1d12 (3 burn Powerful Fist): 216 average (48 min, 390 max)

Seven Attacks (level 16)

• Base die 1d6 (no Powerful Fist): 145 average (50 min, 243 max)
• Base die 1d8 (1 burn Powerful Fist): 180 average (50 min, 313 max)
• Base die 1d10 (2 burn Powerful Fist): 215 average (50 min, 383 max)
• Base die 1d12 (3 burn Powerful Fist): 250 average (50 min, 453 max)

The numbers would go up slightly if you had a higher Strength (Elemental Overflow's bonus really ought to go to it). There's also a potential +1 to +5 on each attack, depending on your enhancement bonus from an amulet of mighty fists, and other possible damage boosts. It's decently powerful damage and good spike damage a few times per day, but it's not going to win the DPR olympics any time soon.

No, because of the action economy

Kinetic Blade and Energize Weapon are both form infusions which must be used as part of an attack action, charge action, or full attack action, which means they cannot normally be used together; a kineticist can only use one form infusion and/or one substance infusion on a single invocation of kinetic blast:

Each time the kineticist uses one of her kinetic blast wild talents, she can apply up to one associated form infusion and up to one associated substance infusion.

With the normal action economy you could only possibly make one of these actions on a given turn so that precludes you being able to invoke both infusions at once, and the kinetic blade only lasts until the end of your turn, so it's gone before you can use it in another attack/charge/full-round attack action.

What if I have extra actions somehow?

If you were to have access to extra standard actions somehow (such as granted by certain Mythic effects, for instance) you could conceivably be able to create the kinetic blade with a standard attack action and then make another attack action with it, applying Energize Weapon with the second action. This does require you to consider the kinetic blade as a "manufactured weapon", but the precise definition of that is contested. There doesn't seem to be specific clarification from Paizo on whether or not the kinetic blade is a manufactured weapon or not, but the similar case of the Warlock's mystic bolt was addressed in FAQ:

Warlock Mystic Bolts: This ability says that it lets me count it as a light weapon, but is it manufactured? Do the bolts add my Strength bonus on damage rolls?

Warlock mystic bolts aren’t manufactured weapons; they’re magical effects (similar to scorching rays or the flames from produce flame), and you don’t add your Strength bonus on damage rolls.

It looks like maybe a kinetic blade shouldn't be considered to be a manufactured weapon, as it is very similar to mystic bolt... but the whole manufactured/not-manufactured distinction is pretty muddy and awful. It seems like it was sometimes used as a catch-all to mean any non-natural weapon, but in others has a definition a little more in-line with standard English. In order for the system to make any sense, some common sense reasoning generally needs to be applied to determine which meaning is meant in context and whether or not an effect is applicable.

Personally, I'd rule that it's okay to combine the two effects if you've got the actions necessary to make it happen; there are worse things you could be doing with extra actions, and it would let you combine different blast types, which is cool.