(1)I don't know of anything that expressly forbids upgrading a composite bow to compensate for greater strength. If I remember correctly, in the real world composite bows are made with several layers of different material glued together. I could see the GM letting you take it to a weapon smith and paying maybe 200 gold to add some new layers and a new string to increase the str of the bow (maybe add a little magic since I have no idea how that would work in real life).
(2)Again, I don't know of a rule that says flaming weapons can't light other stuff on fire (assuming the stuff is flammable of course). As for the shock weapon into water, I'd give it a 5ft radius aoe to shock surrounding targets, and give them a reflex save to dive out of the way.
Disclaimer: None of what I just said is based on stuff from the rule books. It's just my opinion of how it could work, and how I'd probably run it were I the GM. If there are answers to OP's questions in the rule books, I'd like to know them as well.
(1) Adaptive enchantment +1000gp, bow now scales to str of user. Has to be at least a +1 bow of some type to add this enchantment.
I forgot that adaptive was just a flat price not an enhancement.
Where is Adaptive enchantment from? I just did a quick search on the PRD but nothing came up
Also, regarding the +1d6 magic damage, does that triple on a crit? Does my STR bonus from the composite bow triple on a crit? What about my +1 damage bonus from precise shot?
The d6 from flaming doesn't multiply. And precise shot doesn't add damage. The damage from something like point blank shot and the str bonus would multiply.
Why does STR and point blank multiply but d6 flaming does not?
Because extra damage dice (like from the Flaming property, or sneak attack) never multiply. Only static bonuses (like your strength bonus or the weapons enhancement bonus) get added in multiple times.
Multiplying Damage: Sometimes you multiply damage by some factor, such as on a critical hit. Roll the damage (with all modifiers) multiple times and total the results.
Note: When you multiply damage more than once, each multiplier works off the original, unmultiplied damage. So if you are asked to double the damage twice, the end result is three times the normal damage.
Exception: Extra damage dice over and above a weapon's normal damage are never multiplied.