Scott, thanks for the suggestions. As you said, it's a bit late. Fortunately this is not the first time I've touched resin (though not an expert by any means!) and do work with mask for the dust, wet as far as I can, etc.
What I did in the end, was to try the sprue cutters for one big flat part. It caused a bit of a break, so had to glue all up together again, then went for the rotaary tool! Fortunately I have a power socket right next to one of my outside doors and we had brilliant weather, so had the mask on, working ouside. First cutting, then went for the sander and all in all it came out fine! I have now base-coated and put the first grey on, so at least I'm starting to feel like I'm getting going with the model. Still need to open the box of the a/c kit itself!