Amp first approach to building a system, anyone ?

I think, we all or almost all in agreement. At some point you might like your current amp so much that you wouldn't want to replace it.

In my view, speakers selection comes first - if you're into SS amps. Audition speakers of diverse topologies, technologies and brands until you find the sound signature that pleases you most. If you enjoy tube amps, your speaker options will be somewhat constrained to speakers that play well with tube amps.

SS power amp selection comes second, but the choice here is more binary as it revolves largely about gain, speed and maximum current delivery - headroom. Looking at an amp's power transformers' VA rating, power supply architecture and filtering capacitance will often be a pretty good indicator of a power amp's speaker-driving capabilities and determine whether it's a good candidate for an audition - if the chosen speakers are the slightest bit hard to drive, there is no point listening to inadequately sized power amps. As the saying goes, there's no replacement for displacement.

A power amp should not be used as a tone control; it should amplify the preamp's input signal. This is not to say that power amps don't have sound signatures, but the main point is to ensure that said sound signature is synergistic with the chosen speakers'. It may sound like I'm minimizing the power amps' importance in a system, but I definitely am not. The wrong power amps can ruin your whole day (and possibly your speakers).

A preamp, in my opinion, contributes more to a system's end sound than power amps - as it should. The preamp is where the speakers' sound signature is further refined until the desired end sound is attained.

I am in the camp that believes a high-end pre is crucial tò successful system building, and that going preamp-less in a high-fidelity two-channel system (ie relying on a DAC's volume control) is nonsense.

Speakers, amps and preamp constitute the core system. Sources come next, and unless a single source is planned to be used at all times, there is no point in starting building a system from the source.

With one exception. If your main source is going to be RTR high end deck. Then that's where you start. You can also take it with you to audition the equipment. Don't rely on digital source only and even turntables unless it's top level. What will sound great with your perfectly working deck is what you will want.

Yeah, there is no true audiophile system without excellent active preamp, everyone knows it.

I would first select your speakers as that choice can determine your choice of amplifiers.  Very efficient speakers don't require the high power and speaker impedance has some to do with amp selection too.  Efficient speakers with relatively higher input impedances can be driven easily with flea-watt amplifiers such as 300-B tube types and First-Watt low wattage amps for terrific sound.  When I moved from 98db/12.9-ohm speakers to 88db/4-ohm speakers, I had to seriously change amplifiers. In any event, you should choose an amplifier that can provide headroom of ~ 10db above your higher listening levels to allow for high transients (headroom) reducing the risk of clipping.  

My long audio journey over the past 50 years started piecemeal to take advantage of roommates equipment also, so actually first purchase was a TT. Then gradually building system all my own. Then many many individual piece upgrade or experiment.

Cant say I am amp first, though after rolling through several, I have repurchased one of my previous that I end up preferring.

like @pindac  I would say I am polygamous. I have both SS and tube amps, 2 phono preamps, and 2 pairs of main speakers (of different designs).

I find I can satisfy my need for variety while also have well-matched components.

(Also have a herd of vintage components)