Again you should avoid anything that has to do with RNG, randomness is something quite difficult to dealt with for anyone trying to build a competitive team.I think this a good idea! It indeed takes away the RNG aspect while also including all field conditions (rip Gravity lol).
Two additional ideas:
(1) what if the field on turn 0 is random, so it doesn’t always start with Rain/Grassy/TR. Then everything afterwards will be predictable.
(2a) what if the field conditions change once every like 5 turns (so weather, terrain and room simul? This opens up for a bit more strategizing instead of erratically rotating. In some way rotating every turn could be cool, but I would maybe expect a lot of people slapping protect on their mons.
(2b) what if the field conditions chance once every 6 turns, but now weather changes after turn 2, terrain after turn 4, room after turn 6 and then again weather after turn 8. Just a different variant that provides a bit more oversight with all the field condition changing.
I think ideas 1 and 2 could be used together as well. I would love to hear what you and others think about the idea of the rotating field conditions.
Either way, when trying to decide how long should the effect last you may have to ask yourself how long they need to be impactful while not overstaying their welcome, if they last for too few then it may be hard to take any advantage from them but if they last for too long then you may not see most of them and the early weathers may be the only important ones.