Because you said you already have some maxi-balls I won't dwell on the merits of the patched roundball by pointing out that they cost a lot less and out to the limits of traditional iron sights they work just as well.
That said, you should be able to use any powder load between 70 and 100 grains of powder.
I noted that you said you had "Pyrodex 7" and because Pyrodex comes in "P", "RS" and "Select" I will assume you are using Hodgdons 777.
777 powder is measured just like Pyrodex or black powder, by using a volumetric powder measure.
The difference is that 777 is more powerful than Pyrodex or black powder and Hodgdon recommends reducing the powder load by 15 percent if you are using it.
Most production muzzleloaders are limited to 120 grains of real black powder. That amount minus the 15 percent lowers the 777 load to 102 grains.
That said, muzzleloaders are sometimes fussy. They like one or two powder loads and don't like the others. The trick is to find out which one they like.
It's just my opinion but I'm betting that a powder load of around 75-80 grains gives you the best accuracy and is more than enough for any deer in North America.
The tight fit of the maxi-ball is normal.
Because these are not patched they must be a snug fit when they are rammed to allow them to expand and grab the rifling when they are fired.
Some have found that the use of a wad between the powder and the bullet improves accuracy but the bullets were designed to be used without wads so it's up to you whether you spend the extra money to buy and load them.
Accuracy is the most important thing with a muzzleloader so you need to go out and fire as many shots as you can afford to find out what load your gun likes and to dial in the sight settings. Most sight in at about 70 yards because that will allow shots from 50-110 yards without making any special allowances for bullet/ball drop.
Have fun.