Yes, there are 3 ways to activate a level cap:
Just rightclick your MyPet with the item you want them to wear while sneaking.
To remove the equipment just rightclick your MyPet with shears while sneaking.
Weapons/Armor are only visually and have no effect on the MyPet
Riding a MyPet is like riding a horse with a saddle.
Firstly look what you MyPet wants as food here. Then just rightclick your pet while holding the food item in your hand. It will first heal your pet and them refill the Hunger-Points. Every food item has a “substance” of 6points. Every missing HP will use 2points. Every missing hunger-point will use 1point. So 1 time feeding your MyPet can restore up to 3HP and up to 6Hunger-Points.
No. You can only have one active MyPet at the same time.
However you can store pets and switch between them.