Are your speakers efficient?
1. If inefficient speakers now, I would change the speakers to efficient ones I loved, then go tubes, both preamp and amp.
2nd, enough, but not too much power, it effects weight, placement options, amount of heat, and cost of course.
3rd. My order of preference: tubes; hybrid; SS
4. FEATURES. more about preamp, but hard to find in Integrated: I want remote volume and remote balance. I want MODE, stereo, mono, all left, all right.
Note: a lot of modern equipment have remotes but don't show or explain them, and perhaps desired features like balance buried in menus, I had to download and read owners manuals to figure ....
5. easy, safe, metered bias, or auto bias like Carver, others