Welcome bubun! Nice to see you here and researching and getting yourself geared up for your new fish!
Have you already committed to the 4 fish? First off, I would add another fish to make it 5 if you can, Im not a fan of smaller odd numbers, but some people have done ok with a group of 4 but I like to go larger and tend to overstock so take that into consideration. I had 5 wild discus in a 40 breeder for a while and they were doing great, recently moved them to a bigger tank.
I don't think the tank dimensions are that bad.. You have some nice depth and length, the height is fine, its a bit tall but no big deal to me...
I would up that water change schedule. Can you? 10% is really nothing and a drop in the bucket if you ask me... I would try and max out your water changes, especially in the beginning... My wilds seem to do well with less frequent water changes but still big amounts. They didn't seem too keen on daily's, so I was doing 50% every other day. Now in the new tank I am still trying to figure things, but right now I am at about 70% twice a week.
Consistency is key, keep the water fresh and consistent, the more you try and add to it, play with it or distort it in some way, the more room for error and problems you will see...