Pretty simple actually. If you're not gonna log in often, stock up the maintenance in your harvesters, much like you already do for your houses, factories and other structures. That way it doesn't run out between logins.
As for your collections...as Holmes has already mentioned, venders are NOT the way to store things for long terms. Items in the venders have to be renewed periodically, or they get disposed of. Long term storage works far better if you simply set up a few additional houses and stow everything in them. If you're REALLY a packrat though, I recommend setting up factories instead. A single factory can store up to 4000 items(least, that's as high as I've managed to make the capacity in 1 so far) and only uses 1 lot of the 10 allowed for each toon. Simply make sure that there's sufficient maintenance money in them to keep them going long term afterward.
