You can't start your IMC rating until you have got your PPL so that is not possible. The merits of doing an IMC rating if you are going on to do an IR are now not so great in the fact that you won't get a reduction off the IR course. Good practice though.
I see no reason why you can't do your night qualification as you are allowed to combine it with your PPL and it doesn't stipulate how far through the course you need to be - so techinically you could do it prior to starting your PPL (although not practical generally), but in your case it may work out fine. Check with the CAA about this.
You need 150 hours total time to start the CPL (A) modular course. You need 200 hours total time and 100 hours P1 to apply for your CPL.
You need 50 hours P1 cross-country before applying for your IR.
The only licence requirement to start the CPL course is a PPL. If you don't have a night qualification you must complete it with your CPL (so you might as well do it prior to starting your CPL). There is no requirement to have an IMC rating, although you can if you wish.
Hope that helps.