I used to read reviews first (the now non-existent old Stereo Review, High fidelity, Audio). Then a friend said "Have you ever seen them publish a bad review?" Well, Stereophile is one of those that measures the equipment and more importantly listens to equipment at length before issuing a review, saying the good and the bad.

I do go a lot by recommendations from knowledgable sources, such as friends in audio, good dealers, colleagues, and filter their opinions.

Specs are great in getting you the better portion of the gear, but often most equipment have decent specs. I used to look at amplifiers (or pre-amps) and would drift toward on that extends high frequency response to 100 KHz instead of one that ends at 50 KHz. But it does not say anything on how it sounds.

Compatibility between brands is less of a problem than it appears. I typically don't think of this when buying. Only when exotic gear enters the picture, does this become relevant.

For example, most pre-amps output at a low impedance (~resistance) say 250 ohms; most amplifiers have a high impedance input say 10000 ohms or more. Low impedance feeds a high impedance better than the other way around. Most gear is pretty much standard in this convention in that the two are widely different impedances. It's not a concern, unless you run into a pre-amp with a 5000 ohm output and an amplifier with a 6000 ohm input, not likely.

If you want CDs, DVDs players, they output a signal (not impedance) strength at "line" level, just a little below 1 volt nominal. Turntables with magnetic or moving coil cartridges output at millivolt levels, and need a special pre-amp that equalizes the bass and treble and boosts the signal level to "line" levels. These are standardized and should connect well together.

Upgradeability is dependent upon the company. Some allow trade-ins and offer upgrades to loyal customers. Otherwise, if you bought a amplifier and want to upgrade later, it's easily done because the standardizations in place. Same for other equipment. In my particular case, my amplifier does not like reactive loads, so some electrostatics speakers may be too stressful, but most box-type speakers should work.

Note that standardizations do not guarantee great sound, only that the equipment should work together. The quest of great sound is getting gear that is known to do so (from recommendations, reviews, asking this forum, etc.).

Under 2K, look at the recommended components as a start. I'd pick most of the money, say up to 1K for speakers, and the rest for electronics and sources (turntable, CD player, ect.). See what others here suggest.

Without making a long post much longer, I've barely touched upon your questions. Please keep looking here at responses. We are willing to help and enjoy spreading the joy of music as reproduced as lifelike as possible in our homes.