I have several questions in regards to kashering for Pesach
1. If covering Formica counter tops with the white, thick plastic covers, AND never putting hot things directly on the surface but rather on a towel or trivet, is it still necessary to kasher the counter tops?
Not necessary but highly recommended. This is the custom.
2. If i put the stove top grates from my stove into the oven for the self clean cycle, do i still need to cover them with foil for use on Pesach?
Similarly, if we leave the oven racks in the oven during the self clean cycle, do they need to still be covered with foil for use on Pesach?
3. Can I do one round of self clean on my oven to actually get it clean and then at least 24 hrs later do a second cycle to kasher it, instead of me cleaning the inside of the oven?
No need to clean first although basic cleaning is always advised.
4. I’ve always used a small convection oven for Pesach because I heard it was better than kashering the regular oven. But in truth, hearing that we are still allowed to kasher our oven, reminds me that using a proper oven will make my Pesach and Pesach preparations significantly easier. Even though I’ve always used the convection oven, am I allowed to now switch to using my regular oven after kashering it properly? Is it like a neder that needs to be nullified?
Certainly there is an advantage in not kashering the oven.
Under the circumstances this year you do not need to do hatoras nedarim.