Unless you want to get VFR flying quickly, or want a break for budget reasons, Inwould renew both your SEP(L) class rating and IMC then send off all the paperwork together to the CAA, otherwise they will issue you a EASA PPL, with an IR(R) on the back as an expired rating, which you will then have to pay them again to move onto the front of your licence.
To renew your IMC as an IR(R), you will need to do sufficient training, then both the theory exam and flight test, as it has been expired over 10 years.
Whilst your night rating doesn't need any renewing, you would be sensible to undertake some refresher training.
Finally, there have been a LOT of changes in recent years, mostly due to the transition to EASA regulation, make sure your instructor brings you up to speed on these.