chasing the cat and other behaviors

I have noticed a number of behavior issues I have noticed with Mango I thought would have gone away with age but have not so far. The first, and perhaps worst, is his obsession with the cats in our home. We have three, and all are very social. Ever since Mango was little, we always kept gates up so that the cats could have a place to be where he isn't. We have started to take the gates down now that hes older, but we still need to keep at least one up because he continues to misbehave around the cats. Their food and their litter box are in opposite directions in our house because of the layout, so they have to intersect the area where he is in order to get to either.

Whenever he sees a cat, he drops whatever he is doing to go and chase down the cat. He used to play really rough, but he has learned to be gentle (somewhat). Instead of biting he nudges with his nose, but Mango is by no means gentle. Kitties are similar to squirrels and other outside animals, which he needs to learn to avoid in order to be successful. This is why I'm so concerned.

He also still has a problem with walking on a loose leash! He's close, but still doesn't quite get it.

The other major behavior problem is STILL house training. He understands that he needs to go outside, but sometimes cant hold it! And this is for both peeing and pooping. Unless he gets taken out every hour or so, he still has accidents. Leader Dogs recommends I just fulfill this, but its not working at all. Im not sure what to do.