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.