If I go AIO how should I maintain it?
What you described is fine.
Typically AIOs are used for speed work. Even 3D calls their product Speed. They allow for a light polish, perhaps a little bit of filler, and a short lived wax/sealant protection all in one step. So you can get the job done quicker but you're really not getting the best of any single action.
You can do what you asked about. No issues there.
I'm just saying I wouldn't use an AIO if I planned on applying a sealant. I would use a dedicated polish and then the sealant. But there is nothing wrong with what you want to do. People layer sealants all the time. So if you wanted to use Speed's Montan Wax as your base level a protection and then add another sealant on top go for it.
If I am applying protection I would always want my most durable product on first. Then add whatever else on top to either extend protection, add gloss, hydrophobics, etc.
There are a ton a products to choose from. Search around the forum a bit to see what members prefer to use and why.
Right now I'm polishing my newer RAM 1500 with a light polish, then I'm going to use Meguiar's Hybrid Paint Coating to protect it, then I'm going to maintain it with M799 (Meguiar's Hybrid Ceramic Detailer is essentially a diluted version of M799 so that can be used as well).
Really there are so many "toppers" that can be used to extend the life of a base level of protection. Some of these newer spray protection products are more durable then old school waxes and sealants.
I would decide on what you want your protection and maintenance to be (wax, sealant, hybrid sealant/coating, coating) then that might help you to decide on whether you want to use an AIO polish product.
If you plan on applying a coating then you do not want the wax from an AIO on your paint as it prevents the coating from bonding to the paint.