I suggest you do a bit of reading and use Google.
I'll point you in the right direction
Read the tech articles on
This site
Hachiroku.net
Club4age US site so things are a bit different. same rules apply
Bill Sherwood. (billzilla) I found his very helpfull.
I'm on my phone so cbf putting links
Common engine mods swaps
4age 16v bigport into adm models if you buy a JDM model this is the engine it originally comes with
This is the most simplest conv.
All the other 4ages are fwd and will need converting to rwd
Plenty of threads on all these.
4age 16v smallport
" 20v silvertop
" 20v blacktop
Silvertops and blacktops have idependent throttle bodies which can be adapted to suit all the 4ages.
Standalone ecu is best for this setup.
4agze=supercharged
4agte=turbocharged
3sge beams from is200 is another common rwd engine conv. Rather extensive work is involved though.
Ca18/sr20det conv. kits are available
A not so common one in Aus but is more common in the us the f20c from s2000 a lot of work is involved and quite expensive to do here.
This list is the most common and in order from least power full to most powerfull to an extent.
There are also some v8 and 2jz powered rollers too if that is your thing.
Typical Mods include for the 4age
ITBs
Cams can run up to 265 deg on stock ecu
Turbo
Supercharger
Extractors
As for buying your first ae86
Look at condition of chassis ie bent rails
Evidence of previous accident
RUST!
Cheers and goodluck
But seriously read and Google its the only way to learn not everyone is going to spoon feed you because these q get asked all the time.
But by all means ask if you are in trouble at least 1 person is willing to help.
Peace