Okay, there's a lot to unpack in this video.
First is that, your neutral with Valentine all around, it didn't have many/any Deadcrosses or even Air Dashing. You just did double jump into a button without seemingly reacting to much or doing it for any reason. There's a lot ot neutral to explain, but let me sum up Val like this: You should mostly look for 2 things, 1. Hanging back with jump backs and double jump backs and throwing Deadcrosses to make the opponent approach you on your terms, 2. When your opponent is close enough to your range, use things like jHK, jMK, and jHP to hit out the opponent if they take to the air, and do those into either Air Dash jMP/jLK or Deadcrosses to cover yourself if they did nothing and are staying on the ground (to cover yourself as you fall down). When you look at other Val players, try to break down their gameplay from this mindset and see what works/what doesn't (or, how they expand these options) and try to follow the structure like that.
At 45 seconds in, you do wakeup Ground H Bypass. This option isn't realy good for wakeup and should be avoided, mostly because it is not invincible. If your opponent is far away, you don't have to wakeup with anything. If your opponent is close by, you can wakeup with Scalpels Super, EKG super, Level 3 Super, or Counter Super, or even tag, but just don't do H Bypass.
At 50 seconds, and for the rest of the video, you do the classic new Valentine player problem of "pressing too many buttons on your blockstring/confirm". Which is to say, you kept trying to do sLPx3->sMPx2. This is usually bad because it is a lot of hits and scales pretty bad. I think you should practice just doing sLPx2->cMK instead, just so you get into the habit of using less hits at the start of your strings for better damage.
After that, you start just doing Ground Bypasses. If you're going to try using Bypasses, just try to stick to do doing jump->H Air Bypass, since it goes the most distance and lets you confirm.
For Big Band, I have 2 main bits of advice.
1. When you did that initial combo into level 3, you should've have spent that meter if it wouldn't have killed. Learn to forsee how much damage your combo will do at the end before a super before committing to a level 3 like that, and only spend heavily if it will kill. ~Its also important to remember that with Big Band, ending a combo with H A train and/or H Brass results in hard knockdown, so don't be afraid to just end a combo with just those moves if the combo won't kill.
2. You just didn't seem to have any real Big Band combo sequence in mind. Check out the
Big Band compendium and practice the combos there and get the hang of this.