I agree with this. Worms are rare here in piggies. If you have dogs/cats which soil on your grass the piggies shouldn't be eating that anyway. Mites / lice are not a serious problem in the early stages and some people never see them. We've seen them because we bring in a pig from here or there as one of ours has grown old and died, and they come in on the new pig. For this reason some people quarantine new arrivals but as parasites are easily treated here with a spot-on medication (from the vet on prescription) I've just done that if necessary. It's a bit like headlice in children - you do all you can to avoid it then you get them anyway... it's a faff but not a crisis! We've not had fleas, and we've never caught any mites or lice from our piggies either.
I've never used a low dose 'preventative' treatment because the problem of increased resistance when you might really need it is a real one, just like with antibiotics. It's lovely that you are feeling so protective of your new little boars but I'm sure they're doing just great.