Post count isn't especially meaningful; we have many, many vets who have been around for 5-10 years and are too busy with their factions or with other work to post on the forums much.
That aside, there is a lot to consider, rather than solely money and a ship. The most important thing, as in any game, is to have fun. If a faction ignores you, or just impersonally demands things of you without really offering any sort of cohesive community or fun atmosphere, you'll be miserable, regardless of your wealth.
There are many smaller factions that either can't afford to or choose not to pay their members -- most will still provide them with a ship, at least, and perhaps some items, but will otherwise just focus on roleplaying, helping each other out, and trying to work towards some common goal, perhaps in terms of where the faction is headed.
You may be happy in a well-paying faction, or you may decide that it's not as interesting as you initially expected, but just remember that if you find yourself not having fun, you have plenty of other options available. You can try out another faction at any time, and you may meet people you simply get along with better. Most people who do stick around for any significant period of time do so because of their friends, rather than because of their credit count.