No, you should not start out at the Max load.
The best place to start is with a load that is based on caliber, in your case that would be 54 (or 55) grains of powder to match the .54 caliber.
Each gun has its own favorite loads so you will have to find them.
I suggest you set up a target at 25 yards distance.
Your new gun is going to shoot very low because that's how all of the Great Plains rifles come from the factory.
Shoot 3-5 shots with the 54 or 55 grain powder load using the same aim point each shot.
You are looking for the smallest group, not the place the balls are hitting.
After firing 3-5 shots, write down the size of the group. Now, increase your powder load by 10 grains. A lot of people use an increase of 5 grains but we can fine tune the powder load later.
After firing 3-5 shots with 65 grains, again record the group size.
Continue to do this until you reach 105 grains of powder.
By now, you should be seeing some fairly large groups and some small ones.
I'll mention that my .54's usually like a powder load of around 85 grains but each gun is different and your gun might not like that load at all.
To adjust your sights, set the rear sight about 1/2 way up from the lowest setting (if your gun has a adjustable rear sight).
Using your most accurate powder load shoot 3-5 shots and measure the distance from the center of your group to the point of aim. Write this number down.
Now, get out your flat file to adjust the front sight.
If your group at 25 yards is hitting 5 inches low you will have to file about 1/8 from the top of the front sight.
Most people use the shoot a few shots, then file the sight some and shoot a few more shots, then file the sight some method.
When you get it hitting plum center at 25 yards, then move the target out to 50 yards distance.
Your going to basically repeat what you already did but try adjusting the powder up and down by 5 grains from the "best" powder load you found at 25 yards.
Adjusting black powder loads in finer increments than 5 grains usually doesn't do much.
AT 50 yards your gun will be shooting low but if you have an adjustable rear sight you can use it to adjust the groups location.
If you have a primitive non-adjustable rear sight you will have to file the front sight to raise the group.
Have fun.