EX SPD appears to still be strike invulnerable for a short period. LP SPD has more range. MP is about the same. HP has less than EX.
Ultra 2 actually does decent damage. You just have to use it as a punish option. Generally, you pick Ultra 1 if your opponent likes to jump or is a character that bases a lot of their game on jumping. Some exceptions include Balrog, Bison, Dhalsim, and Dee Jay. You can use Ultra 1 to shut down full screen fireballs from most of the cast, but there is always the chance they mix in an EX or you just do it too early/late and get stuffed anyway…
I have a lot of traps, and they honestly are not hard to come up with, so I’ll let previous answers take care of this one. Look for some that leave you in range for SPD and Tanden (at frame advanage) though.
Just mentioning it, but cst.HK, cr.MP is an optimal punish off of Tanden on a lot of characters, and is a 1f link. It is a bit difficult. cst.MP, cst.HP may appear to be flashy but it is definitely one of Seth’s best punishing options if it connects on the opponent. I have no idea why you would think this is subpar, it does signifigantly more damage than any other option Seth has. cr.LK, cr.LP, cst.HP xx HP Shoryuken is a good hit confirm for point blank. cr.LP, cr.LP, cr.LP xx HP Shoryuken works on a lot of characters too and lets you be a little farther away. You can hit confirm all your cross ups with cr.LP, cst.HP xx HP Shoryuken easily.
Another thing worth mentioning, do not get too predictable with cr.MK xx Sonic Boom.
Oh, and some of the “flashy” combos.
cr.LK, cst.LK, cr.LP, st.LP, cr.MK xx HP sonic Boom xx FA2, cr.LK, cst.LK, cr.LP, st.LP, cr.MK xx HP Sonic Boom xx FA2, cr.LK, cst.LK, cr.LP, st.LP, cr.MK xx MK Legs, Head stomp (x3), Dive kick or whatever variation you want.
FA3, backdash, head stomp (x1), j.MP, PP Tanden Engine, BnB