Does the DWE315K take other brands' blades?

Yes. The Quick-Change system fits DeWalt accessories and most standard oscillating blades with a universal arbor. Some very cheap blades need an adapter.

Is it good for cutting drywall and trim?

Yes. The variable speed lets you start slow for drywall and run faster for trim and PVC. Use a fine-tooth blade for clean trim cuts.

Corded or cordless: which should I pick?

Pick corded if you work near outlets and want constant power. Pick a 20V cordless tool if you work on ladders, in tight spaces or away from power.

What comes in the kit?

The kit includes the tool, a carry bag, a wood-cutting blade, a bi-metal blade, sanding pads and a sanding pad holder.

Can it sand and scrape?

Yes. With the sanding pad and scraper blade it handles paint removal, adhesive scraping and detail sanding, though it is slower than a dedicated sander.