Mine has been a sweet boy since day one but I train him the same way I "trained" my kids which I think helps, with a lot of "easy" calm reminders/vibe. Every now and then mine gets an attitude and wants to lash out and I will either put him in his play pen for a quick time out or try and hold him with lots of shhhh easy... Calm words. The timeout in the pen isn't punishmen (we don't use it when he does something bad) and it's different than his crate, but when he's in there he knows he can't go anywhere and it helps him calm down. Mine still has a lot of puppy bitting urges, every day, and we redirect him to a toy or we say no, as he does it and good boy as we are able to pet him without him bitting. Maybe trying to be very calm and trying to ease him down may help?
As far as potty training, we trained our early on to ring a bell when he has to go out. We started it by taking him outside constantly and ringing the bell while we said "outside?" and after a while he learned to where he now runs to the door and rings it hard to go outside. However, on rainy days, he wants nothing to do with outside and has the most accidents. When he has one, we usually say sharply "outside!" and pick him up, even midstream, and take him right outside. Maybe a system for potty training like this could intrigue?
He dislikes having his feet washed too so we limit that to only when he has really dirty paws or steps in his own poo which unfortunately he does often, otherwise we just do a quick wipe. If your dog dislikes paws washed like you stated, I would avoid that as much as possible because it gives them a reason to not want to go outside.
As far has harness/leash, we use all of them depending on the situation. I primarily walk him on a lead rope leash, but when my kids take him out on potty breaks we use a basic leash clipped to his collar (with me, a since I'm his person, a leash isn't needed but with anyone else it's a must cause the other side of the fence is too much of a curiosity), and on hikes we use a harness. We switch it up so much the manner in which he goes out makes no difference for him. Personally I'm not a fan of seeing their neck chocked when he pulls another way, so we leave the lead leash to training walks where I think it has more of an affect where the harness is more playtime outdoors. Maybe using a lightweight leash on every potty break everytime and have one designed spot?