I think 27" TV's is the same as a 25" monitor. It's that whole marketing gimmick where they list the size of the display by diagonal measurement to fool consumers in the retail market. So I think you have the right size. But you'd only want to do the tube swap if your monitor has unbearable burn-in. It's lots of effort.
Surprising that you don't have S-Video on that TV. 3 RCA input is component video. So that TV is a late generation 4x3 tube. Not many were made before component video gave way briefly to 16x9 TV's and to HDMI, then the whole industry went to LCD. So that is a really good score. If you do tube swap, you need a multimeter for sure. You're supposed to test the resistance of the
neck coil yoke to see if it has the right impedance for your chassis. If it does, it is a good candidate for a tube swap.
As for makes and models being better than another, only a few have ever been qualified as perfect candidates for each kind of chassis. This is a secretive art that not a whole lot of people get into. No where near a science. You'll just have to do your homework and hope for the best. Hard to be selective all the way in Alaska with the kind of donor tubes you might get. This is the only site I know that has running list documented:
http://junknet.net/donor-tvs