You have been given some very good instructions for cleaning your musket after firing and you need to deal with the accumulation of fouling. There have been hints of the first cleaning of a musket that has been packed full of preservation grease, but little specific details.
For one, water won't dissolve that grease in the bore and flash channel. You will need your isopropyl alcohol. The leather plug won't really stop the solution from leaking out of the nipple seat and the alcohol can harm the finish. Go to the hardware store and get a plug (8mm -1 according to the Pedersoli web site:
Set 3 nipples for Mississippi, Richmond, Springfield 1861, Zouave (davide-pedersoli.com) ). Use the plug to stop solvent from leaking. Do the soaking of the breech with rubbing alcohol, slosh the alcohol around and dump it out. Remove the plug and use a patch to collect solvent as you run some alcohol soaked patches to verify the grease has been removed. Run a pipe cleaner with rubbing alcohol from the nipple seat to the powder chamber. You can and probably should do this initial cleaning with the barrel removed from the musket. Once it is clean, use an evaporating filming rust inhibitor such as Barricade, EezOx or 2000 CLP to protect the bore and flash channel. Use a never seizing grease on the nipple threads. I suggest that you get a good nipple wrench sized for a musket. Get some good hollow ground screwdrivers that fit each of slots of your screws. Nothing is uglier than screw slots that have been marred because of the use of ill fitting screw drivers.
Black powder fouling either from real black powder or the common substitute black powders is soluble in water. If you use a greasy lubricant on your Minie' balls, add some grease cutting dish washing soap to take the grease out. Water won't remove all the greasy fouling. Some people call that residue seasoning, but it is a layer of burnt grease and fouling. Follow the soap and water wash with dry patches then some patches soaked with either rubbing alcohol or WD40 to displace any remaining water. Now is the time for application of the rust inhibiting film.
With the gun disassembled, look to determine if you will need to glass bed the breech. Most rifles and muskets could stand some glass bedding at the breech. With a solid breech, it is time to apply a decent wax to the stock, barrel channel and the barrel or you can grease the barrel. Note: the water pump grease is petroleum based, but since this is on the outside of the bore its not a problem. In fact many of our favorite lubricants such as Ballistol can trace a petroleum lineage.
Go to the art store to get your linseed oil as hardware store linseed may not have all the driers needed. Linseed oil takes a very long time to dry so apply an oil with driers.
When you load use a volumetric powder measure. All the propellants used are designed to perform to the equivalent of a black powder load measured by volume. On a powder scale, 60 grains of your 2fg Olde Eynsford will be 60 grains. That same measure set to 60 grains will throw a measure of Pyrodex that weighs closer to 50 grains.
Be prepared for some fun.