Firstly, does that allow me to take off into IMC, or should it really only be used as a back up should the weather get bad en-route?
The legal requirement for an IMC/IR(R) holder is to have 1800m visibility for take-off and landing (there's a slight oddity in that under EASA rules you only need 1500m for VFR which can be a workaround in some cases if its borderline).
There's a lot of debate about whether the rating should be seen as a "back up" or whether it should be used - as instrument skills are very much linked to currency (they degrade very rapidly) I personally think it should be used. That being said, there's a difference between flying when you're going to have to do approaches down to close to minimum to get back, and doing so when you might have some cloud en-route to fly through etc - it's ultimately down to the level of risk you're willing to take yourself, particularly if flying single engine, e.g. imagine you're flying on a day where it's OVC008 and the engine fails on you...
Does anyone know what you need in terms of avionics?
I'm not sure what the legal requirements are, but to get the most out of training you're going to want:
* Transponder
* ADF
* DME
* VOR (ideally x2)
* ILS
I'm not sure also if IMC/IR(R) training has to be done under the auspices of an ATO, if so then they'd have to be happy taking your aircraft onto their books as it were...