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You've already correctly identified some methods for HA with 3750s.
As you note, the stack provides "supervisor" redundancy, i.e. if stack master fails, another stack member will take over. One thing to watch for, if your stack master is running IP Services, you'll want at least one other stack member to have that IOS installed (and licensed).
Regarding hosts, ideally if they support Etherchannel/Portchannel to the stack, you can have critical hosts connected to two different stack members, so if one path fails, connectivity isn't lost to the host. For hosts that don't support that, or are not critical, you might have some "spare" VLAN ports in other stack members. I.e. if a stack member fails, manually repatch such hosts to another stack member port. (If fact, ideally, you might have one additional stack member already in the stack, so for such single connected hosts, downtime is the time it takes to repatch [then you work about replacing the failed stack member].)
On the power issue, the RPS would allow usage of a secondary power circuit and it also covers, I believe, failure of a stack member's A/C power supply (those don't fail too often, and if it does on a 3750G, you might need to replace the whole unit[?]). However, the RPS doesn't handle loss of A/C power on both paths (and when it takes over, I also recall, you need to reload the stack to revert off it). So, you might also want to consider UPS too (if other parts of the network might still be operational). Depending how you implement UPS, you might not need an RPS, for example if each stack member had its own UPS and each UPS could be reconnected to another power line.
PS:
For additional stability, if not already running it, 12.2(55)SE8 is considered, by many, as being very stable.
