If Szarel leaves the battlefield at the same time as you sacrifice one or more other nontoken permanents during your turn (probably because you also sacrificed Szarel), its last ability triggers for each of those other nontoken permanents.

If Szarel leaves the battlefield before its last ability resolves, use its power as it last existed on the battlefield to determine how many +1/+1 counters to put on the target creature.

Szarel’s second ability doesn’t change the times when you can play those land cards. You can still play lands only during your main phase when you have priority and the stack is empty.

Szarel’s second ability doesn’t allow you to activate abilities (such as cycling) of land cards in your graveyard.