How many LP's

It doesn't matter whether you listen to 14000 records or 100 if you really enjoy it. If you listen to classical music, it is easy to quickly accumulate many records, if you don't and are quite selective then probably couple of thousands would be more than enough.
I would start with 100 used records and inexpensive but decent turntable and then decide what to do next.

This would be my list of first ten records:
1. Miles Davis - Bitches Brew, original 360 sound US or Canada pressing or original Japanese pressing.
2. Mahavishnu Orchestra - Inner Mounting Flame, original or reissue Japanese. If you can't find them - original British, German or Dutch pressing.
3. John McLaughlin/Paco de Lucia/Al di Meola - Friday Night in San-Francisco, original Japanese.
4. Al di Meola - Cielo e Terra, original Japanese, original non-DMM US, Dutch sound good too. 
5. Dead Can Dance - Into the Labyrinth. I am only familiar with original UK.
6, 7, 8. Pink Floyd - Dark Side, Wish You Were Here, The Wall, Toshiba Pro pressings if you can get them, other Japanese and some European pressings.
9. Deep Purple - Machine Head. Only heard original Japanese non-pro - pretty good.
10. Paco de Lucia - Siroco. Any you can find, Japanese is best. Analogue recording, digital mastering. Sounds half analogue/half digital. Paco's best album in his and my opinions.

It may be true that most of us listen to about 100 different LPs in rotation, no matter how many LPs each of us owns, but I posit that in order to develop that 100-LP rotation, you need to own at least 1000 or more.  More is better. This makes it possible to go outside the rotation once in a while for a test listen to either a new musical genre that is under-represented in your regular rotation, or a new artist, etc.  Once in a while the experience is such a revelation that the LP breaks into your list of the regular 100.  As a result, you now have a regular 101, or some other LP gets knocked off the regular rotation.

I've got about 2500.

What technology is best? I vote for air bearing, although a prominent and expert guru (Ralph K) disagrees. Even so, I'll bet he'd like my system.

I use a DIY air bearing TT with a Trans-Fi air bearing arm, playing a Koetsu platinum cartridge. The air bearing TT replaces a Nottingham Analogue unit, which has been updated, and is essentially a Dais. Which I recommend. But not as highly as the Trans-Fi arm, which is $1000 and plays with the best.