Before you can decide what to shoot thru your rifle, check the instructions for the rifling twist. If it is 1 in 60, you are going to need to use patched round ball. A 1 in 48 twist will handle either round ball or conical bullets fairly well.
Cleaning? No , you don't have to remove the barrel. There are suppliers who sell fixtures that screw into the nipple hole that have a rubber hose extending from the fitting. Simply put the hose in a container of soapy water, and use a patch on a cleaning jag to pump water up into and out of the bore. This will clean it up fine. Be sure to dry it completely, and oil or grease it afterwards.
Fixed sight rifles are adjusted for elevation by filing the front sight. Usually it is left high on purpose, and sighted in by filing after the proper load is found. Filing the front sight RAISES the bullet impact on the target. Windage is adjusted by drifting the rear sight in its dovetail.