I suspect you can remove the cylinder head without removing the engine from the bike but can't swear to it. If you have a factory service manual, it will say for sure. On newer bikes, like yours (I working on vintage bikes), the valve cover generally has reed valves built in so in order to remove the valve cover, you may need to remove the reed valve covers and hoses. You will need to remove the carburetors, etc. Generally, the valve cover can then be slid to the rear and removed. Once off the bike, you will see your cam chain which likely is not center mounted. It will have some sort of tensioner which will need to be removed. There will also be a guide called an idler assembly on your cam chain... once those are off, you remove the bolts holding your cam caps in place. The cam caps retain your cam shafts. It is generally a good idea to put the 1 & 4 cylinders to TDC at this point as it makes reinstall of the cams easier. After removing the cam caps, you can slide the cams out and will have to tie up your cam chain so it doesn't fall down into the engine.
Once the cams are out, I am not sure if this is a water cooled engine but if it is, you had best drain the anti-freeze and remove any water lines going to the cylinder head and then remove cylinder head stud nuts... there may be a couple of 6mm bolts on the ends that need to be removed as well... a shop manual will give the exact steps...
Once everything is removed, you pop the head on all sides with a rubber mallet and then find the pry points suggested in your manual and work the head up... it may seem stuck as the head gets stuck to the gasket below which is stuck to the cylinder block.
Once the head is off, you can disassemble. The factory manual will give you MAX valve stem lengths with the valve stem inserted in the guide. This stem length is a good indication of wear on the valve seats. Use a digital caliper to measure stem length (the end extends out for measuring depth). It is hard to determine valve guide wear since most of the guides I am familiar with have only a 7mm bore width. I can tell if there is excessive wear by rocking a valve in the guide (after disassembly) sideways but if you haven't a feel for this, you may want to just go ahead and replace the guides with the seals. If the valve lengths are not excessive (outside spec), you can probably clean the combustion chambers and replace the guides and seals and then lap in the valves prior to reassembly.
Disassembling the valve train isn't all that hard if you have the correct adapter and a valve spring compressor. The adapter will be the same size as the bucket where the shims are retained. There is a Kaw special tool (adapter) I am sure but you may be able to buy an adapter and compressor in the aftermarket. You compress the valve train which makes the split collets accessible and you can fish them out with a small magnet and/or tweezers. Once the split collets are off (also called split keepers), the parts are come apart. I suspect you had best keep an eye on the valve springs as they may be directional... windings may be more dense on one end and there will likely be two springs; one inside the other. Replace all components where they came from.
Anyway, the job isn't all that big a deal. I would suggest before you start tearing apart the head to consider a leakdown test to verify the source of the oil and crud... it is a bit unusual for seals to make that much mess. The problem may also be the piston rings... Might save you some money to diagnose this issue properly before making assumptions on the valves/head.