Hooray! A fellow rally build. =D
So, not sure if you plan on running actual rally tires, if so 16" tires are going to be hard to find. Almost all teams run a 14-15" gravel set up or a 17-18" tarmac setup. I have seen 16" rally wheels and tires, just hardly any. Rocky Mountain Autosports sells Black Rocket rally tires that come in 16" (
http://www.rm-autosports.com/black-rocket/ ) but they are pretty wide, 205/60/16 and 215/65/16. I'm 80% sure they will rub at that size. If you're just going to run more street style tires, you'll be OK with 16".
If you do plan on doing some off-roading I recommend to go with 15". Cheaper, lighter, more choices of tire and... "More cushin' for the pushin'. " per say. Plus used rally tires (aka, take-offs) will be easier to find and buy off rally teams that don't need them anymore. Or new ones too.
Currently, I'm running 15"x6 steelies with DMACK DMG2 (175/65/15 [G42-medium]) and they are great in the dirt. On the road they can be pretty wobbly when changing directions. I'm sure anyone that has run snow tires on 15"s knows that feeling. I thought since the DMACK's have such a thick ass side wall it would eliminate that wobble... but no. I assume that's why all tarmac rally car use 17-18" rims, to eliminate that wobble. If you plan to do more autocross type stuff, just stick with a larger rim and smaller profile tire. I use the stock rims and tires for autocross... they do good enough for me and I keep up with cars in classes above my own. xD
Also, as far as rims go, here's my 2 cents...
Steelies are a great cheap place to start... plus you only need to buy three. Heavy though... (edit: Just weighed mine with the DMACK's on them, 44lbs each. Stock wheels were 39.4 lbs)
Team Dynamic and Briad are top notch, but a bit pricey and (for me) hard to justify since I'm not in any competitions.
Oz/Sparco are good choices, especially if you want that signature look. (Try Emailing Team O'neil and see if they have any old OZ wheels to sell. They are really cool guys.)
Method Rally Wheels are my personal favorite and what I plan to buy. A good mix of strong and cheap (compared to TD and Briad) Subaru has been using them on all their rally cars for a while now, which sold me. Right now they only have the MR501's in 4x108, But I've been told they are working on the MR502's as well.
So, it really depends on what type of driving you plan to do majority of the time. Hoped that helped at least a little bit! =D
Some other good rally type sites to look at...
http://www.specialstage.com/
https://www.teamoneil.com/