I’m thinking about starting to play this but since i’ve been playing Sf3 for like 3 years i really don’t know where to begin. What should i think about? Tactics from SF3 that doesn’t work here? So far i really miss the parries 
Start from scratch. No, “tactics” from SF3 dont work here. Parries are retarded. Its called blocking and knowing when to jump over a FB.
lmao no parries for you, son!
space control, footsies, meaties…you can still translate some of that over here.
although you don’t have an “easy-mode” defense like parries, there are specials that have invinciblity that goes through stuff.
welcome aboard.
Read this: http://gootecks.com/the-3rd-strike-players-guide-to-street-fighter-4-by-gootecks/
Most of it can be applied.
And approach the game as if you’re always fighting an Aegis ready Urien.
I think 3s can actually help you a little here. Although somethings will get you killed. The two main things (for me) that are different are throwing and combo timing. Not only is the command for throwing different, but the priority is different. Use strong to throw unless its a free throw (strong has higher priority). Also, learn to flip out of throws. It will save you a lot of health.
Next, get really deep for combos. Go into practice mode and just relearn you jump in timing.
Overheads/high low guessing, aren’t as much a big deal in this either. Pretty much always block low unless your opponent has and likes his overhead.