I think one aspect we still need to know is whether we will be able to make individual claims on each character or planet. The current alpha allows one at a time regardless of numbers of characters. It may be possible for someone to fill up their own town if they can make a claim on each character. Personally, I don't want to see claim per character happening. I would like if it's possible to make claims on multiple planets however. It would be really rough to play a beastman if your only claim account-wide is on Tartaros for example. (Perhaps this issue can or will be circumvented through guild storage and buildings? Max 1 individual claim per account would not necessarily be max 1 guild?)
I believe there will be checks in place to prevent gaming the system like that, meaning that real people will be needed to upkeep and maintain towns, purchased or created. Spreading a small population across many towns could weaken a guild instead of strengthening it. The guild could focus it's membership to a handful of towns, but that would leave the rest weakened against any opposition.
So my answer to you after much rambling @Alexian is that the requirements to make a multi-town guild work are very high even for preformed guilds. This game seems to give the best benefits to a guildtown governor who is also the guild leader. A compact single town build is a very strong start, with the possibility of branching out later. This along with the scale of fractured means that multi-town guilds can also be strong with a good community, but are not likely to sweep an entire server under their wing.