Big tummy - can only be done through diet and exercise. Or rather, as my son so lovingly puts it, put less in than what comes out and move about inbetween. Keep a record of weight or inches or how clothes fit. Don't set high aims just because it is New Year. And don't make food such a big issue. Leave something on your plate. Get used to smaller portions. Eat healthily if you can but if you do want something sweet or richer, have it for a meal instead of a pudding. Drink lots of water. (Not with the whisky! ).
Decluttering. Boxes, and lots of them. Bags for bin and charity. Boxes for storage and things you need now. Do a room at a time, label everything, and maybe break the time down into manageable hour sections so you don't get bored or too sore if you hurt a lot with pain. Make lots of brews and put some music on. Buy some lovely boxes to keep memorable items in or paperwork (I have a lovely metal box for birth certs etc). Shred any documents which are of no use. Be ruthless. If you don't need/use/like it, bin it. Or sell or give things which someone else can use.
Going back to work - Make a list of all the things you need to do in preparation for going back. Prioritise the things on your list and do them in the order they need to get done. If you start earlier, you will have longer to get ready and you will feel better that you are not running about on the last minute.
Lastly, come on, get off your tush, get it done, the party is over (for a while at least). Attention! Up two three, out two three, tidy two three, list two three. Motivated now? Good.