If you've used Maptools in the past, maybe keep at that. I have been using that for a while an are fairly familiar with the tool, though I don't really use all the features (like lights or fog of war based on tokens and stuff. I just block out the stuff the players aren't supposed to see until they complain they should be able to see something by now.

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Character Sheets everyone had their own however they liked, for Initiative i have an Excel Sheet.
The biggest prep work for my D&D 4 and my D&D4-based/inspired homebrew Star Wars campaign so far has been making maps for encounters. I like to make it big. It's a good idea to build a repository over time of NPC/monster tokens, furniture, textures and the like.
I used the old offline Dungeon Tools for my D&D 4 campaign.
Another GM has been using Roll20 for a longer Dungeon World campaign. That worked mostly with theatre of the mind, so we mostly had a big map of the region we travelled through and only occassional some encounter maps. But Dungeon World combat is so bare bones/simple that it doesn't matter. The neat part was that there are also Dungeon World character sheets for us players, so we could manage our characters completely inside Roll20.
Currenly that GM is running a Pathfinder introductory game, and he got a Pathfinder adventure to play that with. Apparently at least for this adventure, there was a Roll20 content pack (for money, seperate from the adventure itself) and that came with maps and other stuff ready-made for use.