Look at that - it's part 3 already (even if parts 1 & 2 aren't quite ready for the printer)
These parts are so interrelated it's hard to say what should be covered first, but I still feel that having some separation will make the process easier.
OK - everyone wants a pool that is as unique as they are. However, if you are DIYing it for the first time, perhaps KISS (Keep It Simple Stupid) is the best way to go. You are learning new skills and the margin for error is small! To make the project as easy as possible for a first timer - I recommend a flat out 16 X 32, 18 X 36 or 20 X 40 pool with either 6" radius corners or 2' radius corners. I suppose you could do a kidney pool, but getting any 'funkier' than that is asking for headaches. (these days, you can design about any shape you want with seats and tanning beds - but that's best left for the pros to install) I would avoid grecian pools because the corners can be a real b**ch to get right (but I will help anyone who wants to install an irregular pool - it's just not going to be in these threads )
You need to ask yourself what you require from the pool - do you NEED to dive, do you want a heater, how many lights, how large a shallow end, waterfall, SWCG, safety ledge, etc. I strongly suggest to anyone who wants to build their own pool that they ask Mark (mas) and Jason (Lion) about the proposed plumbing and filter set up!
I'll assume a straight up rectangle with stairs. AH yes, the stairs - it will be easier for a first timer to have the precast fiberglass stairs (if only because it makes dropping the liner a LOT easier) - they have a little extra work on the install, but are easier in the long run.
With regards to the liner, IF you know the dig will go without a hitch (like hitting bedrock) you can order it with the pool kit - they can take 3+ weeks to come in so it's better to have it before you start the project. However, if you all of a sudden have to change the floor - you'll be stuck with an expensive piece of liner that you don't really have a use for. If you are doing a 'sport' or non diving pool, this probably won't matter. If you have the liner before you dig and install the bottom, you MUST stick to the dimensions they cut the liner to!, if you wait - you can tell them what to cut the liner to. 8)
Again, I'm only trying to start the discussions with these posts - I'd LOVE some feedback on what I've said -- and then we can really start 'filling in' these posts