Many of these probabilities can be looked up in official statistics. Then you can adjust a tiny bit depending on whether you think you have more or fewer risk factors than the average.

When I feasibility tested by asking my wife to guesstimate a couple of these she ended up very close to official statistics. The first-level trick she used is Fermi estimation.

You can totally do it and it's worth practicing. There are even competitions in it open for anyone! I like the Quarterly Cup at Metaculus. The next iteration starts early January.