Gearbox isnt really an issue, up to you if you want to swap the box for different one. All the gear ratios for various different boxes are in the FAQs or about on the forum. A quick search should find them.
Dan's guide on putting a 1.4 16v in a cinq is a good source of info -
Clicky
I assume you want to run it on a mk1 16v ecu (commonly refered to as the 18FD), I've uploaded a wiring diamgram on here somewhere. Search my posts and youll find it.
No real difficulties as such, depends how much time and money you want to spend on it. You could spend years and years (and far too much money) like myself
or just swap it over in a weekend
Best to refresh engine mounts or stiffen them up with a little bit of tiger seal or something similar.
Can't run with the cambelt cover and the bolt for the O/S headlight will need filing down.
O/S engine mount might also need a little bit of material removing from it to stop the alt belt catching.
Can use a larger throttle body of a 1.6 engine or some rover TBs.
Exhaust you can use the mk1 exhaust manifold and then get an exhaust place to make you a down pipe and join it on to the system of your choice.
There's plenty of info on this section of the forum and a few choice search words will help you sift through nearly a decade of people trying different things.
Don't forget that putting a bigger and thus heavier engine can also change the dynamics / handling of the car, so make sure brakes / suspension are in good order.
This is by no means an exhaustive list but not sure what else you want to know
