First of all, get a shop to do a diagnosis of the problem, just to be sure that you're fixing the right part.
How long you can put up with the car being off the road, and whether you can set aside some time to do it, also needs consideration. If you find a good replacement tranny or an exchange deal (rather than repairing yours) then you might get the car back the same day if you give it to them whole.
Ask whoever would repair the tranny what the saving in labour cost would be and decide if it's worth all the hassle of tackling it yourself.
If you do decide to remove/install yourself, then I'd allow 1 day for removal and 1 for refitting if you haven't done it before. If you have done it before then you could probably halve that time.
A tranny shop would do this considerably faster (probably 2 to 4 hours total for removal/refitting) so the cost saving may not be worth all the hassle. You'll also have some comeback on them if the install wasn't right.
Personally, I've never done this on a P10 but I have replaced the clutch on my Mitsi' turbo and it ain't rocket science, just a lot of greasy hands, an occassional skinned knuckle, some sweat and maybe some swearwords.
If you decide on, and feel confident about, doing it yourself and have the tools/info/resources needed then there is no reason you couldn't carry out removal/refitting.
I strongly recommend Haynes manual #1851 for 1990 - 1999 Nissan Primera. It has an excellent procedure (w/pics) for removal/refitting of the manual tranny. Your local library may have a copy, otherwise it's not an expensive book. It has some helpful tips like - it's not necessary to undo the driveshaft retaining nuts at the hubs (you can just free the inner end and place it free of the tranny). Unless you're experienced, I suggest you obtain a procedure to guide you through.
The only "special" tool I can think of that you'd need is a ball-joint seperator tool.