For something like this I don't think a particular style is as important as repeatability of the wort, as you said. I'd just go with a very simple, 1.5 gallon base recipe for an APA, maybe something like this:
Size: 1.5 gallons
IBU: Varies (30-45 for APAs)
2 lbs -- Brewer's 2-Row
1 lb -- Toasted Malt (just roast 2-row in a 350F oven for 10-15 minutes)
Mash Schedule; Single Infusion, Medium Body
Mash-In: 152F ST (1.25 qts/lb) for 60 min
Mash-Out: 168F ST (2 qts/lb) for 10 min
Sparge @ 168F
1 pkg -- Safale American US-05; rehydrated per instructions (Ferments pretty clean and crisp, also cheap compared to liquid)
With this recipe you could just purchase a single 50lb bag of 2-row and make your own toasted malt (being sure to roast it exactly the same each time). That should get 16 or so brews out of a single bag making your learning experience relatively cheap. I'm not sure you would want more than 1 gallon of beer at a time (assuming you lose 1/4-1/2 gallon to trub, so about 10-12 12oz bottles) while learning about different hops, but you could scale it up to 5 gallons all the same.
You may also want to check out adding hops to the mash, as is discussed here
. I've done it on a couple of brews and it does add a nice hop aroma and flavor without the bitterness masking it in lighter beers.
As far as hop choice I'd check out this handy chart I found and go with the flavors you like the most: http://www.brewerssupplygroup.com/Fi...pVarieties.pdf
. It has most of the hops on there and I've used it on every brew I've planned out.