I mean, I guess do tones, because it won't take you too long to get the idea. After that, tones will be part of vocab, so you'll have to work on it continually.
Yes, focus on tones (and pronunciation in general) so you don't have to go back and relearn all your vocab to pronounce it properly. If you don't focus on tones, you'll sound like my third-year classmates talking about how chest hairs love to eat bamboo.