TL;DR most new lawyers who try to do the hybrid hourly/contingency structure fail
I should have been more clear. Do a hybrid of flat fee and contingency fee. I hate hourly fee structures. They suck. They are highly inefficient. I don't use them unless I'm defending a small corporate client. Your corporate clients are really hard to get, but once you snag one, you better do all litigation for that client because they are going to come to you for everything. You won't get bogged down with hourly litigation work because you won't have that many corporate clients, if any, when starting up.
The retainer is a form of a flat fee. Depending on the laws of your state and depending on whether you comply with those laws, your retainer may actually be a fee advance. Either way, do this at the beginning only. The hourly contingency fee hybrids are dumb because the percentage is too low. Lawyers who use this aren't good. They aren't confident they are going to win. That's why it's so important to be proficient at litigation. You have to win to get paid. If you are not proficient with litigation, you have to resort to having a volume litigation practice where cases are settled often before are right after a lawsuit filing.
And it's a gamble. Your only concern should be the fight. But being proficient allows you to settle cases in the early stage of litigation. The amounts won't be a whole lot. But they will be enough to last you for 6 months or so. Once you get better, you can settle cases in the later stages for more money. Or you can just go to trial. Of course, your client has final say, but they often follow your recommendation.