There isn't a magic level of illness at which it's fine, IMO, because that isn't what will make the difference to what happens as we open up. Before we fully open up, we need to be at a level of immunity, rather than illness, that means rates won't just inexorably rise again. For me it's about keeping illness rates level or going down, not going up. We need stability to manage covid.
It's all very well having foreign holidays and care home visits and routine surgery and so on back because of testing - if the testing is constantly picking up cases because we've let rates get high again, then those things still won't be able to happen. Hospitalizations and long covid are still things we don't want to increase too much.
For me the key question is : are we opening up at a rate that will keep covid cases roughly stable, because increasing vaccinations will keep a lid on it and balance out the opening up, or are we going a bit too fast, and getting ahead of vaccinations, so rates of covid will start growing again?
I'd feel reassured about the rate of opening up if I trusted people to also voluntarily keep doing the distance, ventilation, mask things a lot of the time, even if not all the time, but people seem to see it as all or nothing. But the fact is we really need those things to be doing some of the work of keeping a lid on covid rates, alongside vaccination.
And yes, variants are a big worry as the wrong one could undo all the good of the vaccination programme. Again, keeping rates low by a mixture of measures including ordinary people not abandoning all precautions at once is what we need.
I'm not competely sure if we're going too fast or not, but those are my concerns.