...until the 8th January. Now obviously this means I'll have been away for more than 1 month and I have full intention of coming back to the server when back. HOWEVER I don't want all my belongings and land to just vanish because of the inactivity.
...
The period for your land to be reset in the wilderness is 3 months, but this can be extended if you have a valid reason, but as you're only away until mid-January this shouldn't be an issue. You will have to discuss things directly with your town but I shouldn't think it would be an issue and since I'm so late replying this is probably too late to do so now anyway.
...
Town membership, plots and money: 12 months.
...
The actual towny details last for 12 months (so being listed under '/resident'), your town itself might have specific rules plots and town membership though; so you'll need to check with them. If you are town staff you need to be much more active than that though otherwise your position will be lost and possibly passed on to other staff or willing residents.