4-5 people isn't nearly enough to finish the project in a reasonable timeframe. Keep in mind, we want to cover a whole modpack, not just a few mods. Even if we take a more reasonable modpack like horizon, there will be a ton of mods to cover and not everybody in the team will be able to build 24/7.I'm fairly sure you have the man power, and I imagine each room will take a game session to complete if each individual person does one at a time, also you are underestimating the length of the wait. If all modders were updating to 1.7 then we'd likely have the next pack in July, however 1.8 isn't even out yet and given the track record of FTB the 1.8 packs won't be out until December. That's a hell of a long time. If you wait that long you'll start losing interest and therefore manpower.
For example, a mod like thaumcraft would take me at least 2-3 weeks to cover all aspects in bite sized chunks, not counting the time needed to make everything look nice. And there are far more complex mods out there, that will take even more time.
Personally, i would rather start sooner than later, for the same reasons you pointed out. But you underestimate the actual work that has to be done on this project. It's not like the FTB maps, where you have a set of goals and you have to figure out how to get there, they are much simpler (for the builders). And even they had a much bigger team than just the currently 4 team members of LAM.