Just finish my first playthrought yesterday and I had similar doubts about how to spend the points, but did not ask/read about to avoid spoilers. I will try to give you some spoiler-light tips.

1. I can't say anything specific about those weapons because I did not use it (I built a melee/energy weapons charachter). Sometimes I missed a strong weapon to deal with flesh enemies at distance, then the launcher could be an option. On the other side, if you have some spare points, I'd go for exotic weapons, you will find some intersting stuff later on (that is, if you are getting points in research, too. If not that would be useless).

2. No. There are a few situations that require Hacking 6, but they are not essential. And don't waste your ICE-picks on these, too. Save them, really.

3. Point-wise, I see no reason to improve Cyber affinity instead of getting this Psi ability first. The Cyber affinity bonus is just used in timely situations anyway (I don't think there are cases you need a minimall requeriment, like with others), and you will find plendy of psi-hypos.

4. I played with Psi ability of 1 and no Psi Power. No problem at all. It is a very interessant alternative path, but you can save it for the next time. And then you can get all the booze you want to recover a few health points. ;)

5. Well, that just depends on how are you playing, but I think Strenght is indeed very useful (save ammo with melee weapons, bigger inventory, several armor and weapons have Strenght requeriments). Mainentance is very useful, too, and there is a minimum requeriment to use the skill in heavier weapons. You can repair and modify every weapon you find, or fully modify one with French-Epstein devices and stick with it the whole game. It is important to know that there are NO auto-mainentance tools (that do not depend on your skill), while there is auto repair, modify and hacking stuff (the items are rare, sure, but they exist).

On the other side, as I said, higher Hacking is not so important. There are very few situations in the game when you need to perform a fast hacking (and that's what you save the ICE-picks for). On general, you can just restart the hacking process until it works.

Enjou the game! It is really amazing, and there is a LOT of stuff to come yet. ;)