Heya,
The Yn622's have their reputation for a reason, inexpensive for some good, reliable triggers that work across a lot of systems, and do TTL, HSS, etc. I use my Yn622's on my TTL capable flashes (YN 565EX II's), as well as with my portable wireless strobe (Rovelight 600B). Having a little system that can easily grow and do TTL, HSS, etc, reliably, is fantastic.
As for which flashes to go with, that's up to you. I very rarely use TTL off camera in a multi-light setup, but that may just be my own personal use. I find when I'm doing a specific shoot, I control all output, so I just use everything in manual. The only time I use TTL is when I'm just bouncing light and I have no option for a 2nd shot and want to get it as close to right without having to take time to find the right exposure. I also use TTL off camera when I'm just playing with my kid outside or something like that, where she will be closer or farther away, and so TTL is nice to help adjust for that quickly (and I just dial down EC to blend).
Which flashes you get basically depends on the features you want, and what you are willing to pay for in terms of your preferences (ie, focusing on slightly higher output at 1/1, consistency of color, how many shots at 1/1 you can manage before it's too hot, etc; as well as of course, the features like TTL, HSS, etc, if you really need them).
So far, I use Yongnuo 565EX II's with TTL on some YN622 triggers, off camera of course, and I can fire pretty quickly with a battery pack attached to help recycle times and how often I can shoot at higher powers before needing to replace any batteries. And that setup per flash is $100 for the flash an $30 for the battery pack. I have two of these and so far I've been quite happy with the performance on battery pack when I'm out and about, as I never worry about running out of juice, or missing a shot due to recycle time being too slow (when doing a spontaneous shoot, where I'm not able to control everything, think 2 year old).
Very best,
