You should have minimum 5 ft but 6 ft is ideal. I've played pool where tables are 4 ft from the wall and it is too close. The standard pool cue length is 57" and the draw length is about 6" so 5 to 6 ft would be ideal.

Personally I think you are better to wait until you can afford to put back an in ground pool as the one's that I have seen sitting above the ground look like an eye sore - a temp pool - that looks like it could collapse at any time. Maybe while you save for the bigger project you could rent / buy a large Spa Pool.

I'm glad you guys are growing.

We have had a vinyl lined pool for 15+ years - you are making a good choice. They need no maintenance or resurfacing etc. Ours is an Aqualux liner in Caribbean. http://www.aqualuxpool.com.au/colour-range/ This colour is just the right amount of blue/green to sparkle and shimmer, look cool and inviting, but dark enough to gather and retain the sun's heat. I ran a swim school for many of those 15 years, and needed a pool that could take the knocks of hundreds of children each week, and look like something they wanted to dive into. Any lighter and the pool would look too cold, and darker looked scary! I have friends who chose the darker colours for their heat retention properties but the pools don't look as inviting, and algae builds up quicker but is harder to notice until the levels are quite high, so needing more chemicals to control/eliminate.