Classic Which should play first Classic or Modern wow?

I remember in 2014 I was playing a private wotlk server and remember getting to lv 80 but I never got to do raidsand with the announcement of shadowlands and classic I have revived my interest in the gameWhich one should I play first? Classic or BFA / Shadowlands? Also what should I do to buy BFA and then Shadowlands? or wait until shadowlands realase and then go up to lv110 and then buy shadowlands? via /r/wow https://ift.tt/2EPQ7D0