Since I'm the first one up this morning :>) I will give some quick thoughts. Hopefully others will chime in with more details.

1. Bead/cove or beveled edge won't make any difference in your finish choices. You still want as good a fit between strips as you can get no matter the finish.

2. Wider strips can be OK in certain places. As long as a fair curve can be obtained for the glass cloth to lay down tightly. The finish- varnish or paint - won't make any difference here.

3. For fillers you are right that color matching won't be necessary if you are going to use paint. But matching or not matching should not make any difference to the ease of speed of construction.

Whether painting or varnishing I think the construction methods would be nearly identical.