"This would take me to 175TT, but I need 200TT for CPL license issue(?) Do I need to hour build that 25 hour gap to get my CPL issued?"
Yes you would
"It occurred to me recently that it might be a good idea to do the IR before I do the CPL? This would mean I wouldn’t have to hour build that 25 hour difference for CPL issue, is that right"
Yes its is. Lots of threads debating if its better to do the IR before or after CPL.
"If you are only intending to instruct, why bother with the CPL/IR? Neither are required for PPL instruction under EASA. The theoretical knowledge for CPL is still necessary, however"
True but with a PPL you need more hours before you can start the FI course. The cost of that extra hour building is about the same as the cost of doing the CPL course.