Yes if you want to go fast and not do too many reviews at once you need to always prioritize radicals and kanji. You can find more in-depth guides in these forums if you want.
More generally not finishing the vocab of a previous level before starting a new one is not bad in my experience, it spreads out the exposure to a given kanji on a longer period and reinforces it more.
Try not to have vocabulary lag too far behind however, if you’re level 7 and haven’t finished with level 4 vocab then something is probably wrong. You don’t want to accumulate a huge vocabulary backlog.
If you want a very in-depth explanation of the mechanics and how to “game” them, see:
Note that I absolutely don’t recommend to aim for a one-year level 60 speedrun, but going as fast as you’re comfortable early on is certainly very valuable. Those early kanji are extremely useful.