“Mashers” - people tend to get frustrated by this shit a lot. You have to understand first of all what you can punish on whiff / block, and what you can’t. Sometimes it is possible frame wise, but you can’t react to it fast enough. That’s fine, you just need to learn to back off until you can see it coming better. It’s better to let it slide instead of go for it too late and eat shit because of it. A lot of people say they know how to punish, but there are literally thousands of situations and not even the best players knows every single one down to the pixel (example moves become more/less safe i.e. spiral arrow depending on the spacing) most good players DO know what “looks” punishable / not. Keep in mind every move has a different amount of hit/block stun as well and you need to change your timing depending on when your character exits this state.
to bring this all back home, i’ll give you a solid example. someone who mashes lp DP from a reasonable distance away. you stick out your far normal, boom you just got hit by the 2nd one. What would I do? Let thme build that miniscule amount of meter and wait for the next one (the better your reactions get the better you can snag these) you can almost guarantee the next time he throws out a random lp DP he will do a 2nd one to try and bait you a second time. now you’ve just conditioned him to stop that bullshit. this is actually not even a scrubby tactic at all despite what people will tell you. Smug (best dudley) will whiff DPs all the time against me to build meter because he knows how hard it is for me to chase it down.
When to Combo:
First of all, forget about complicated combos. take that shit right out the window. Figure out every single thing you can do first try without thinking and add this to your personal “arsenal”. this includes single button presses and making a mental note about how fast and how far they reach, right down to your ultras.
Now you have your arsenal built, you can determine whne and where to use these.
so the most obvious is a whiffed ultra / HP DP / EX tatsu from goken where you have all day to react and input whatever you want. Keep it simple - if you have ultra stocked, use it. If not, you should have something hopefully starting with a jump in if you have time to get that little bit of extra damage. Typically with Guile, I will just do cr MP flashkick and throw the jump-in in if I have time. like i said - keep it simple. the extra 10 points of damage is not worth dropping the combo.
advanced punishes : example Honda’s headbutt. It is -10 frames with a medium headbutt, but it bounces him back soo far. all you can snag him with is a cr MP. however, you can combo into an ex sky high off a cr MP, so if you have the meter, get that damage! you will find many situations like this where maybe all you can get is 1 hitters, but you can’t leave free damage like that on the table. understanding all your standard blocked punishes is super important.
next you need a light confirm. you will find yourself in situations where you are crouch teching or maybe you just scored a jump in but you arnet sure if they can block in time or not. you will need some variety in these normally as well. with Guile, I have charge and no charge situations, just like Vega. so my no charge situation is (ideal to start with a low because it forces them to block crouching, extra chance to hit) cr lk, cr lp, st lp, st HP. some nice damage, and a safe block string. if I have charge, then I will do something like cr lk, cr lp, cr mp xx flash kick. or if I am not entirely confident I will hit the link, then I will switch flash kick with a boom (or just had no down charge)
on top of that, you need to be able to mix up to get even more damage. slight delays in your block strings to catch them pressing crouch tech (frame traps) are important, but only if you have conditioned them to eating throws. Vega really excells in this because he has an excellent kara throw so he gets many ticks before he needs to commit to the string ender (throw or trap) using buttons specific to beating this is huge (Vega can mix in his overhead, Guile has the upside down kick)
The rest of your game will mostly come from pokes, kara throws, and possibly a few gimmicks /shennanigans (most of the best Vegas just play solid footsies though because of his sick range and fast pokes, fast walkspeed, great jump speed + jump arc and dont want to risk the unsafe stuff) so vega actually does not really rely on combos as much as some of the other characters, he relies actually much more on the setups that come off the block strings.
Hope this helps and anyone can feel free to correct me or add in more information where necessary!