Is it just Class 2 with a hearing requirement?
Yes.
Would anyone who's added an IR to an IMC give a recommendation on where to do theory and where to do flying, how long it might take (I can do full time)
Suggest you visit (and join)
PPL/IR Europe if you're not a member already. Lots of valuable stuff there.
and whether it's worth doing in my SEP or go straight and do it MEP?
What do you intend to do with the IR? If you're going to be flying SEPs I suggest getting the SEP-restricted version. These days you have to do a renewal in an MEP for the IR to remain valid on MEPs, so if you're not flying MEPs on a regular basis there's not much point in getting the unrestricted version.
HTH