If your bearings are that worn, they should be humming quite a bit and quite loudly. The car should also coast less than a car with good bearings and feel more sluggish than normal as speeds increase.

With the car up and the wheel off, stick a wrench on a bare spindle bolt and spin the hub as fast as you can. Then sit back and listen. chunk-chunk-chunk RRrrRRRrrRRR both mean bad bearings. Swshhhhh is what you should hear.

Rotors and calipers have to come off. Buy new cotter pins and use them. You're 80% there that you could at least pack fresh grease into them or inject grease with a gun without driving them out, but you should just do it right and pull them and inspect them if you're unsure and think they're the problem. Then, if you have to replace them, you already have everything apart.

Cheers