Help with first tube amp

I would recommend sticking with amps that are well reviewed by Stereophile, The Absolute Sound, and HiFi+. These are highly respected professional audiophile reviews. I would start with their annual component summaries. You will find brands like Cayin, PrimaLuna, Audio Research, VAC, etc.  well reviewed. I would not hesitate to buy used of one of these brands although I always buy new. Other off or "amazing sound" for a budget cost... only new. 

There are too many risks buying off brands. Try to listen to a couple different brands... typically they will have a house sound, reproduced through their component lines. In the less expensive lines PrimaLuna, Cayin, and Rogue (I am personally not a fan of the the later). But all are well regarded. 

Tube watts are much more powerful than solid state watts. So while 25 watts of solid state power are unlikely to sound good on your speakers 25 watts from a good tube amp will probably sound great. Assuming you’re not into headbanging music at hearing loosing volumes. 

2.    ⁠Are my Sonus Faber Sonetto 1 G2s at 87 db sensitivity a good match for these lower-power tube amps ?

no, my beloved Cayin A88T is only 45wpc in ultra-linear mode. I would look to get 75 to 100 wpc tube amps, (try, option to keep or return).

or, change your speakers to more efficient ones, with larger woofers, so you don't need to add a sub or pair of subs.

Where are you located ______?

finding used floor standing speakers close enough to drive to, listen 1st, .... both enhances success and keeps the cost down

I would want to know more about these Focals

https://www.ebay.com/itm/187546278611?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338381866&toolid=10001&customid=6759478a-8b45-11f0-b442-346135396336

In response to the post by @ghdprentice, the Pass XA 25 is a great sounding and very capable 25 wpc ss amp, and I understand your Cambridge is no slouch. Tubes are not for everyone. There are pros and cons living with each. It boils down to you and the sound characteristics you are looking/listening for. It is all subjective, and listening/reading reviews is not the answer, ime. Honestly, folks who love tubes, ime, like a bit of warmth, color and politeness in their recorded music reproduction, and there is nothing at all wrong with that. Tubes tend to be very holographic, when matched well to the rest of the system (in this case, the speakers). I prefer sharper attacks/transients, finer detailing, along with strong, rhythmic and controlled bass, and of course, an extremely quiet noise background. At 71, I have been through lots of gear, and I simply know what I like, as do many others, although, many still play in the merry go round, of changing gear (part of the hobby). This is the key...determine what you like, by listening, with your ears/brain. My best, MrD.

https://www.stereonet.com/forums/topic/541045-best-speakers-for-tube-amps/