Any metal workers find the 2amp motor adequate for taking down the occasional weld or brush finishing stainless tube (using good belts of course) ?

Yeah, it’ll take a steady diet of weld grinding. I’ve been using 80 grit. Just let the tool do the work without much down pressure. Very good tool..

Would this help get tough to sand parts of my hardwood floors?

I was a professional carpenter, served a 4 year apprenticeship, have worked on residential, commercial and industrial projects, including hardwood floor refinishing. I retired from the trade in 1989 (it sure doesn't seem that long ago!). In short, this is a great sander, but it will not work for what you want. Go to a rental store and rent the appropriate equipment. Above all, have a top notch vacuum at your disposal.

Would this tool work for sanding recessed areas in cabinet doors? We are stripping kitchen cabinets.

Yes, its currently what I'm using it for and the reason I bought it. HOWEVER, make sure you use the lowest speed and a grit no coarser than 320. I first tried a 120 and it started eating right through the wood. I switched to a 320 and it worked good to remove the paint and nothing else. Use a light hand as well.

Can the filer handle sanding a small plastic while a very small amount of continuous stream of water is pouring over the sample, for cooling?

Don't believe the unit is made for water cooling.. Water may be thrown into the motor. You might be better off looking for a different cooling agent. Air for example?