Builder vs ID - landed 1st floor extension plus reno

[purpledino 1]

Hi I know there is a thread on ID vs builder vs architect but I still have some questions so I’m posting a new theread.

just got a 70s inter terrace for which I would like the following done - extend first floor built up by about 25 sqm, shift toilet fitting position, major internal reno 

I contacted my previous ID who did a very very good job with my condo reno but he is a one man outfit.

would actually like to continue with him as he provides very good service and follow up. And he offers good suggestions to reduce costs. However not sure if this is too much for him to handle (given there is extension). Should I be engaging a builder instead?

Thanks.