If it does happen on roll20, I might ask for players to help fund a gamemaster's membership for me to help make for the best experience. This would allow me to get all the goodies that make online tabletop games great. Based on my current experiences with roll20, I'd probably want to use Skype for communications.
But I do have a complaint. "D&D meets Twilight: 2000" was a way of giving a quick analogy for the game's setting, not a promise to mash two entirely dissimilar games and settings together. The setting I'm planning is a take on the Battle of Manzikert, fought in 1071 between the Byzantine Empire under the Emperor Romanos IV against the Seljuk Turks under Arp Arslan. In the real battle, Romanos was betrayed and captured. Arp Arslan asked his royal captive what he would do if their roles were reversed. "Kill you, more than likely." was the reply. The Turkish warlord told Romanos that he was going to something much worse: let him go.
Historians point to that battle as the point where the Roman Empire began its long slide into ruin. It's also a great setting for the type of game I want to run, a game where the characters are already established, and have an immediate, pressing, need to work as a team to survive.
Thinking about it, the campaign could take several paths, all of which could run into each other with some meta-plots running in the background.
First of all we have The Long Road Home. This is the most basic concept. The characters, after coming together in the wake of the rout, decide to work their way back to civilized lands. It's a reasonable goal, and would make for a fine episodic campaign. The push is obvious, survive to reach home. The pull could be a desire to expose Constans Logios as a traitor, or to raise a new army, or to just get back to normalcy. All sorts of fun roadblocks to throw here, and a recurring foe in the agent of the enemy sent to hunt them down.
Secondly, the players could decided to be the Merry Men of Cappadocia. They steal from the evil and give to the good. The area where the battle took place still has many humans, now enslaved and forced to farm and labor for the enemy. They need heroes to save them! Again, this would a good episodic game. The characters would need to find a safe hide-out, gain allies, and then begin striking the enemy where it hurts. This would also lend itself to a running villain. I like boss fights at the end of a campaign. This one would require a more detailed map of the area the players will be operating in.
Next, is the Lawrence of Cappadocia option. Forget raiding, raise an army among the locals and wage guerrilla war against the oppressor! I think in this case a more constant style would work as the characters work to recruit their army from local nomads and lead them to victory. While fun sounding, this one might bog down into a wargame, and I haven't read the mass combat rules yet. But still, it would appeal to players who want to change things on a larger scale.
Then there's the "Run In The Wrong Direction" possibility. Like the first, it involves getting away from the battlefield and heading home, but in this case, the characters are forced further and further into unknown territory until they have a much longer road. I really like this concept, because it gives me a chance to really do so world building on a grand scale in a fantasy realm. Keep pushing east and you come to places like India, Southeast Asia, China, and beyond. How do you ever get home? Admittedly, this option is the hardest for me as a game master, as it would require a ton of creative work. Plus, the players have to agree to a railroad for the first couple of adventures. Still, if you like road trips. . .
I can absolutely see these ideas merging. The campaign might start off with trying to get home, then coming to the defense of a small village and sticking around to protect the locals, who eventually form the nucleus of a resistance. If that resistance is shattered, the crew might find themselves many leagues from any known landmark and hunted by an army.
All good stuff. I'd be interested in seeing what people like from these ideas.