Triple to compact doable ?

Very doable.

My commute bike with Shimano 105 5700 was a trilpe when I bought it and I converted to a double. It's fine once you have adjusted the limit screws to make the change to what would be the smallest ring a ghost shift.

I’ve read that you can do this. Googling suggests setting the inner limit screw to not allow the mech any further inboard, along with some advice on using tape or glue or something to keep your ferrules in place if you do shift too far down and slacken the cable.

There’s clear advice not to set it up with small and middle and winding in the high limit to prevent it jumping outboard, as this can bugger the internals of the shifter.

I'm pretty sure you can do this. I think (and Shimano will confirm) that the triple shifter can be used as a double with no issues. Simply set the middle shift as your inner ring and the outer shift as normal. You can get a ghost shift (and the cable goes slack) if you click down too far but you will get used to not doing this. Is the new 105 chainset 11 speed? If so you would need a new 11 speed chain  - it will work fine with the 10 speed cassette (unless it has seen some decent mileage and will need to be replaced if this is the case to avoid skipping).