I would agree on one point that no one brought before.
Exhaustion. I will tell you right now that even though Team for UMVC3 was HELLA HYPE at NEC... it went on for WAY too long for some reason. And the extra hype caused people even spectators like me to get exhausted. I can't imagine having to play tournament matches after going through that the next day. People were way more on point that day than the next day and there were only 2 Weskers in the top 3 teams (essentially only 2 Weskers in a 9 player pool). When you are exhausted you are much more prone to drop combos and get hit by stuff you are unlikely to get hit by normally... ie dominance of Wesker who has undroppable combos and easier execution to help you through an exhausting time phase.
I felt there was a definite difference in quality of play from the first day to the second day.
You can assume you have an abundance of meter, if that's important.
Karsts I would recommend the following characters for your team:
Zero
Viper
Vergil
Dante
Trish
I feel one of these 5 characters is going to be what you are looking for. Here's a breakdown of each character:
ZERO
I think he is the premiere point character in UMVC3 right now. He doesn't need assists to get his game started, just need them for combo extension purposes (which you have Dorm Dark Hole for). Most of the choice point + assist selection you go against, Zero can easily get past. He definitely gets mileage after Dark Harmonizer as a Sogenmu'd up Zero can beat anything in the game and pressurize for days against the best of characters. The most trouble Zero is going to have is against full on zoning team with space covering projectiles against which you have to time Buster -> Lightning with assist calls to catch them on the happy birthday. He can also play lame and space out while calling Dark Harmonizer. Ton of meterless damage, lots of priority and get in options while being fairly self reliant.
VIPER
If she has meter she can blow through a ton of point + assist set ups by just using EX moves on demand. With Dark Harmonizer on deck this enables her to do thus. If you are capable, you can attempt Seismo spam to keep assists at bay or Seismo plus Optic Blast or simply buy time to call Morrigan. There should be DHC synergy between Viper and Dormammu. She will eat up a ton of meter but it will be meter well spent. She is easily one of the strongest characters in terms of pure defensive options which is what you are looking for. If you are up to the execution challenge, then I would definitely recommend this character on your team.
VERGIL
I personally would not recommend this character be played without a good horizontal assist on the team... and the only exception is if he has Dark Harmonizer on deck. Simply put, if Vergil has meter to blow he shouldn't have trouble against anything because he would overwhelm the opposition by just burning meter. Devil Triggered Vergil is easily a top 5 character and has trouble against virtually nothing. The same can be said for him with Summoned Swords. Dark Hole can cover him and set up some left/rights but on this team Vergil basically wants to one man show with Dark Harmonizer. DHC synergy should be fine as well. Vergil should be able to use Dark Hole for combo extensions with Hightime as well. You would still need to play exceptionally well defensively with Vergil and buy time with Round Trip/Judgment Cut for Dark Harmonizer calls. As a bonus, Rapid Slash would be ideal for Dormammu as he can extend combos with it easily in the corner (since he can now wall bounce to get to the corner easily during combos) and Rapid Slash on block pushes them ALL THE WAY FULL SCREEN.
DANTE
Pretty much the same as Vergil only he is more capable I feel in this team set up. He can go Devil trigger if he wishes to and Dark Hole allows him to do the one thing he badly needs... combo off of air throw. He can play against numerous match ups and Stinger Reverb Shock into Fireworks is a great harassment against many assist calls. He is self capable in spacing and buying time for Morrigan assist calls. DHC synergy should work out as well. Nothing much to say here except this character fits well on that team set up but it's Dante... he's good on any team. I am sure Jam Session would be a great asset on the team if you ever need it.
TRISH
Another solid pick for the team. Trish and Morrigan is a tried and true combination where Trish can just super jump, set traps while calling Morrigan. Trish loves meter on deck and can pressure opponents with Round Harvest. Her overall point game is strong and she can handle multiple match ups. She can assist punish with Max Voltage into Chaotic Flames. Dark Hole covers up space for Trish and that's about it, nothing substantial but she doesn't need it so it's not a big loss. Out of all those teams that you are worried about... I would be wary about Vajra and Hidden Missiles teams vs Trish. Other than that Trish with meter should be fine. Peakaboo assist is great on any defensively heavy team.