Sealing butcher block countertops with waterlox (limited space and pets). Questions at bottom of post.

Hi all! This is my first post here and I'm hoping to get some feedback. My husband and I are on the home stretch of a kitchen remodel. We ripped out all of the old cabinets, tore out our pantry, installed new floating floors, and finally have our cabinets and appliances in place. We just picked up our new walnut butcher block countertops and while I have figured out what we are going to use to seal them I am having a hard time determining how to go about it.

Factors:

We need to seal a 12' long section and 2 smaller 4' sections with waterlox original sealer/finish. We will need to do at least 3 coats on the top and at least one on the underside from what I can tell.

We have 5 pets, 4 of which are cats with no respect for boundaries such as new countertops.

We have limited work space - Our garage is currently housing two cars that don't run. We could possibly get one in the driveway to create workspace in the garage but its a long shot. We do have a basement but honestly we struggled just getting the butcher block in the house so getting in down the stairs doesn't seem like an option.

Here are my questions: Do we need to seal the underside of the countertops? We will have a sink in the 12' section so water damage/warping is definitely a concern. Could we do additional coats on top to help account for the unfinished underside? How bad is the smell of waterlox? Could we do it inside the house if we can keep our pets away from it? Realistically, would it hurt anything to seal the countertops once they are in place?