Heya Ellie,
Fellow T Slimmer here ! I get loads of bubbles so I just continuously tap the vial and squeeze air out until it looks goodish, tbh I don't have a massive issue with bubbles as you still prime the fill and so I just wait for a few drops to appear before confirming, it's no issue imo.
Yes insulin resistance happens with higher levels, I find my threshold is around 11 mmol/l and will ghost carb to nail it, I think a low carb situation can make this worse as the lower I have been with carbs the harder I find resistance with higher levels and so any extra protein will add to this level of pain. I think alot more research is being done around high levels/insulin resistance as there are contributing factors to the insulin resistance wall we hit when taking insulin and the way exercise/diet/weight etc affect it, so it's a personal experience but felt by many of us.
I don't do sleep mode as my pump will naturally bring me down to around 6 mmol/l over night, I haven't used it for night time as I think the bottom range is increased for overnight protection, i've not found it necessary to use sleep mode.
Yes your target BG should make a difference, mine is set at 6.1 as I need a good buffer for driving, i've never tweaked it down as don't want to run lower.
Hope that helps.