What is required has been discussed thoroughly on this forum in the past and doesn't merit repetition. If you're having trouble finding appropriate results with the
search function let me know and I'll help you dig up some threads. (Yes, I really need to get a concise thread put together for the FAQ section... So little time...)
I don't know anyone who's purchased a JDM engine for a MKIII from any shop other than DriftMotion recently. I don't recommend JDM engines. Particularly when an engine reaches this age it's most likely in need of a full rebuild regardless of mileage. Save the money on shipping, buy locally and save yourself the headache of figuring out what's different in the JDM 7M-GTE and trying to then locate those missing components locally. A 20+ year old engine is a 20+ year old engine.
Getting an engine, electronics and transmission of the same year or revision as your car ('87 or '88 in your case) will save you a good amount of hassle too. Otherwise you're likely to need to swap subframes, sensors, oil pans, patch even more wiring and so on.
If possible getting a complete front clip or a complete donor vehicle will be a great help too... This way you get all the mounting brackets, the intake plumbing, the oil cooling system and so on.