I usually fill mine to the upper line. Check and verify the level using the dip stick because as I mentioned earlier, the window isn't always accurate. Also make sure the bike is on level ground.
Those long dome nuts are part of the fastener pattern that holds the crankcase halves together. Looks like you may need an impact wrench to get those drain plugs out. I have an old electric Black & Decker one that works really well .....
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