you could prob use the boost then, since levelling can be quite slow imo. achievement points come from mostly just playing the game, exploring/doing JP, PvP, doing story journal. dailys give 10 AP, you can see the panel which one is more interesting for you to do.
base game is free to play with some minor restrictions like chat/tp. try it yourself and see.

HoT zones are still pretty active, core Tyria my be a little quiet. Malaysian guild i know HAX is quite active, CCTV fewer ppl now. i recommend playing on NA realm since there are SEA/Oceanic players there. i am on Sea of Sorrows NA, which server u pick is mostly for WvW, PvE doesnt matter which server.