UPS Pickup Question

I’m new to this so bear with me. I’ve always done fbm and am trying my first fba product. I want to get this correct as I have a lot invested in this product and want to limit my mistakes. I have 10 20x20x20 boxes going to 5 Amazon warehouses. When I go to request a UPS pickup I don’t see anywhere to say how big your boxes are that need to get picked up. Will they just show up and take that many large boxes? How would they even know if they’d fit? Everywhere I read says they’ll pick them up no problem but I still have this uneasy feeling they’ll show up and be like “I don’t have the room for all those.” My 2nd question is, besides the no placement fee for sending your fba inventory in 5 shipments, have you noticed any other advantage? Thanks in advance for my rookie questions!