here... this talks about the entire swap (from a 4a-fe to a 16V smallport 4a-ge.... will talk about similar issues as a 20V, but doesn't go over much wiring seeing how i used stock wiring & ecu)....
my complete swap cost me $1600 including: 4AGE motor, new flywheel, MSD 6al, MSD blaster 2 coil, MSD 8910 EIS tach adapter, KBD header, corolla GTS radiator (new), SARD adjustable fuel pressure regulator & gauge, new cap, rotor, spark plugs, oil, oil filter, belts, new KBD header, thermostat, radiator hoses, GTS gauges (from junkyard), & a couple sensors i had to buy, high flow cat, cat-back exhaust piping and exhaust done at a shop.....
http://www.cardomain.com/memberpage/219038/9even though the blacktop is map based and would be easier to work with boost.... the blacktop has lighter internals and it can't handle nearly as much as a silvertop can (which i've heard is lower than the 16V's can withstand... especially the gze which have partially forged internals)...
you could also find a map based 4a-gze ae92 if you look close enough... which is pretty much optimum.... there's another silvertop car (an mr2) around here, which dyno'd at 120hp at the wheels... i put down 109hp at the wheels..... (just in comparison) between mine and coomers, i spent about $1400 less, have 4 less valves, ~200 rpm less, non vvt motor, but have a stronger head and easier to fix & upgrade (in the US) motor....
once you have the motor in, you can do what you want... your stock tranny (assuming your celica is an ST) will bolt up to any A series motor (probably even a 3a-c).... you won't need any custom mounts (although, if you go to a G head you need to bolt your 7a-fe motor mount bracket on the 4a-ge block instead of use the 4a-ge one... the upper part of the mount is slightly different and has timing cover clearing issues)... but as far as accessories read what i talk about in my above link.... i go into depth