Sixty millilitres is light for a 40mm tyre. Go to 80 or 90. Sealant will not stop a burp but it stops a burp turning into a full deflation, and yours is probably getting thin anyway.
Top it up every three months or so in a dry climate, sooner in the heat. Shake the wheel next to your ear - if you cannot hear it sloshing, it is gone.
Worth saying too: some rotor and pad combinations howl in the wet forever. That is not a fault, it is a material choice.
Bed them in properly and then stop listening to them for two weeks. Half of all brake noise threads are people who have started paying attention to a noise their bike always made.
Chain and cassette, and your checker is already telling you so. Just under 0.75 on an 11 speed is well past the point where the small cogs are gone - they have the fewest teeth sharing the load, so they wear first and they are the first place a stretched chain skips.
The test is to fit a new chain only. If it skips worse in the small cogs immediately, the cassette is worn too. If it is silent, you caught it in time. At 6000km on 11 speed it is nearly always both.
Indexing is not your problem. Cable and B tension issues cause hesitation across the whole range, not load dependent skipping in two cogs.
Check the hanger anyway while the wheel is out, it costs nothing to look. But a bent hanger does not care which cog you are in.
Then buy the chain and stop worrying. Keep a spare quick link in the saddle bag.
Chain now. At 0.5 on 10 speed you are well inside the window, and 10 speed cassettes tolerate more chain wear than 11 or 12 do.
The maths: three $30 chains over roughly 9000km beats two $95 combos over the same distance, and it spreads the cost. The only reason to wait would be if this cassette has already run past 0.75 once, in which case it is already compromised and you would be buying a chain that skips.