Sweet find here man
My advice as a fellow E30 owner would take the engine, box / diff from the 325i and bolt them in, AND the suspension and brakes, the standard 318i stuff isn't catered for if you want to tune it and the front stuts from the 318 are the smaller 48mm type, when the 325i will probably have 51mm struts and Bilstein shocks to boot
Bushings will be worn out more than likely and it's well worth investing in Polybushing the subframes, diff and front legs. I did mine and it tightens the handling up so much, the 325i antiroll bars will fit too.
E46 rear top mounts are a factory fit mod and a Z3 1.9 shifter which bolts straight in for a factory short shift that's less than half a B&M one at £26 all in!
I know that's a lot there to be said, but if you spend a little out and some time spent in transfering all the goodies over from the 325i, you'll have a car that'll perform really well and have cost you pennies in relative terms to tune up and a good basis for further tuning if you want to go futher
