2) Have not taken off the cassette (Is there another way to take off the cassette without a chainwhip? I’ve got the splined socket tool for removing it but I don’t have a chain whip and it’s a pain to drive the nearest bike shop 1 hour away on a good day with no traffic…)
Suprise your LBS, and ride maybe it is a bottom bracket. If it was a steering issue you would hear, and feel it when your turned. Also when you bounce test the bike do you hear anything ?