advice needed on 1st real stereo system

Go with the amp that sounds the best. 3db is all you're going to gain by doubling the power. As Elizabeth noted, we typically listen in watts and milliwatts, not tens and hundreds of watts. That first watt is the largest increase in spl you will ever experience no matter how powerful the amp is. In fact, a 1000 watt amp is only about twice as loud as a 100 watt amp. Smaller amps of quality tend to be better than their big brothers in terms of overall performance imo. They're quieter, faster, with more resolution.

Everybody is giving you good advise. As a first timer, system set-up ; particularly getting the right speakers positioned correctly; is going to be your most challenging task. If you don’t have an experienced friend to help you, then a qualified dealer, who will spend the time necessary to see the installation through, will be worth the extra expense of buying new.

Thanks again everyone - hugely helpful all around.

Today I listened to a Rotel RA-12 vs Peachtree Decco with BW CM1s. Slightly preferred the Decco (fuller, richer sound), but then the Decco started smoking! It was pretty crazy...

We were playing the system pretty loud so I asked if the amp blew out, but store guy said the speakers would have blown out first, so didn't know what happened. I am now very hesitant to buy the Peachtree despite the great sound...

I would check the archives on the Peachtree quality also check for dealer support in the archives if both are good I would not worry about a single incident (but that is a weird one - even though the B&W CM1 is 84db and 5.1 min imp that should not happen)

A 20 X 20 room is going to be a bit of a challenge. Choose your speakers carefully, and you might want to consider some room treatment. With all due respect to the other posters, while highly efficient speakers with their lower power requirements might at first seem like a good idea, please keep in mind that often that efficiency comes at the cost of reduced bass output, which in turn might have one looking at the added expense of a subwoofer(s). While I'm not against the notion of a speaker with high efficiency, I've yet to be satisfied with what's been offered. Low powered tube amps tend to cost as much if not more than higher powered ss amps. Again, choose your speakers first, then select the appropriate amplification for those speakers.