Are there still field moves

Damaging Z-Moves don't make accuracy checks

Similar to moves such as Swift, all damaging Z-Moves skip the accuracy check, meaning they not only have 100% accuracy, but also ignore changes to the user's Accuracy stat and the target's Evasion stat. Furthermore, Z-Moves can even hit a target through Protect and similar moves, though they only deal 1/4 their usual damage in that case.

Status Z-Moves simply add an extra effect to the normal move, rather than creating an entirely new move. It sounds like the extra effect from being a Z-Move applies before the normal effects of the move, so they presumably always work, but the normal effects of the move would still be subject to accuracy if the original move was (e.g. Z-Toxic would always give +1 stage Defense, but might fail to badly poison the target).

Source: http://www.serebii.net/sunmoon/zmoves.shtml

The effect of the drinks increase with Isle Evelup's level. All the following values are per session.

Drink -- Level 1 -- Level 2 -- Level 3

Level Boost -- 100 exp -- 200 exp -- 300 exp
HP Boost -- 1 EV -- 2 EV -- 4EV
Attack Boost -- 1 EV -- 2 EV -- 4EV
Defence Boost -- 1 EV -- 2 EV -- 4EV
Sp. Attack Boost -- 1 EV -- 2 EV -- 4EV
Sp. Defence Boost -- 1 EV -- 2 EV -- 4EV
Speed Boost -- 1 EV -- 2 EV -- 4EV

However, I'm not sure how the other exp effects work in conjunction with Level Boost. So this only answers the base part of your question and the question in your comments.