Some of the following powers are more general, others were created specifically for a construct race. I'm curious as to how you would rate these custom powers in terms of cost.
1. Enhanced speed: base movement speed increased by 30. Based on the running proficiency, I'm guessing this is worth roughly one power. Increasing past this might be +1 power per 30 movement increase to a max of +120 movement speed. Notably, spell like abilities can make you twice as fast for an hour an an action once/hour.
2. immunity to gas, charm, hold, and sleep. Harder to peg, maybe half a power each?
3. immunity to mind control or form alteration. Probably 2 or 3 each.
4. (21+ minus hit dice) spell resistance. Probably 3-4 powers. Increasing base spell resistance is probably expensive.
5. Flat damage reduction. -1 damage suffered to a minimum of zero. Nothing bypasses it. Probably 3 powers. Against a specific type of damage it may be 1 power for 1 point of reduction per die (ie. 6 powers for 6 points of fire immunity per die.)
6. Immunity to fatigue. Probably one or two powers.
7. Immunity to curses and energy drain. Probably 1/2 power each.
Yeah Running is a good baseline to compare against. I would be a little worried about very high speeds being more-than-linearly good (ie, +60 foot speed might really be worth 3 powers instead of 2). The big balance concern is interaction with armor and destroying the tradeoff between “go fast” and “be safe” in dungeoneering play. Running, notably, doesn’t work in heavy armor.
Initially I thought a half-power might be reasonable for each of these individually, with elf/elven bloodline paralysis immunity as a benchmark, but then I realized that the elf text says it’s only immunity to paralysis from ghouls, which is more limited. Throw in immunity to poison too, though, and you have the undead immunities, which are a full * for monster XP purposes (comparable with cleric spellcasting in power, which is 500 XP, versus 5 thief skills for 400 XP). On that basis a think a full power for each of those immunities might be justified. Immunity to disease and fear are also each a full power (as Divine Health and Strength of Spirit). Wakefulness, which lets you sleep four hours a night, is also a full power - I could see immunity to sleep and not needing to sleep at all being two powers on that basis (double wakefulness).
It might be worth considering whether saving throw bonuses to particular categories of saves (Save vs Death, Save vs Spells?) could get you “close enough” to your desired outcome; save bonuses seem more idiomatic for the B/X classes than immunities.
These are quite broad; one thing I like about (say) the undead immunities is that they’re pretty specific about which effects they make you immune to.
Lairs and Encounters lists magic resistance of 20-HD as worth one XP * for monsters, which is probably about 4 powers, yeah.
I don’t think there’s a precedent for unbypassable DR, even among monsters. -1 damage per die from each of edged, piercing, and blunt weapons would be about three powers, and might get around the 5HD clause that comes with resistance to nonmagical weapons.
The Endurance proficiency sort of does this already; I agree one or two is probably OK. Is there some other fatigue effect that Endurance doesn’t cover?
Curses is somewhat broad - does it cover the effects of cursed items, or just Bestow Curse? Immunity to just Bestow Curse is probably worth more than a power (constructing it as a Protection spell, it would be at least second level and the duration can only go up to 2 hours, so you’d need to spend a turn every other hour to keep it up, or take multiple powers to be able to cast it in a round four times every eight hours, and an innate immunity is better than a spell-like ability because it can’t be dispelled). Immunity to energy drain is a very significant ability, since energy drain never stops being a threat at high levels, and usually you don’t even get a save. I’d go with at least three powers, probably more.