Goretex( i presume you mean fabric!)

Your leather boots will get sodden and stay that way.  At least when your fabric boots get wet and the sun comes out they will dry out  quicker. 

If your stay high up there will probably be snow on the tops in places.  There was last year when I was up there.  It will probably be soft and melting by then though. 

BTW you can drive right along the windy road (not good for suspension) edge of loch Arkaig and park near the gate at the end.  It's a great place and I'm jelous.  There are plenty of streams all over the place so water should not be a problem.  I know a couple ov exceptionally good camp spots in the area.

May is the best time to go as midges will not be too much of a problem.  Watch out for the ticks though!  They are a real B******.

You will get wet feet!

The light footwear for evenings is a good idea - I tent to go barefoot which probably isn't clever.

There were quite a few flies about near the beaches so if you are not staying in the bothies it may be worth heading to higher ground to pitch your tent. 

I got wet feet for venturing off the paths...

I went last May, no snow except during a four season ascent of Meall Buidhe although there was a dusting of snow on the munroes the day we left, the day that the TGO challengers arrived. Went off trail a few times over sodden ground but never had wet feet. My boots are Scarpa something or other, lightweight with reverse leather and fabric uppers and a Goretex lining. I've forgotten the model designation, they have M3 sole units but seem to be discontinued now. Really good boots.

I've found them, Scarpa New Peak GTX.