A couple of bags of petits pois (not proper full sized frozen peas) in a pot or large bowl (ahead of time if possible to allow them to thaw) - boil a kettle of water and pour over a few minutes before serving time. That is enough to cook them, especially if they have already thawed, and doesn't need a ring for cooking them.
How many ovens do you have? Can you have one for the turkey and another for veg and bits? Or juggling all in 1?
Cut veggies small, to cook faster. So for oven roasted (root veg, or Mediterranean mixed veg), dice them into 1cm chunks rather than 5cm chunks you might normally do as more rustic versions. Yes, takes more prep time, but less time in the oven when it's under pressure (so maybe 20 minutes once the turkey is out and resting, rather than 40-50 minutes - and may even allow you to juggle roast potatoes in and out, and throw veg in to cook while you eat starters).
This might sound daft, and I haven't tried it out, but perhaps doing stuffing into well buttered muffin tins in advance and cooking until mostly done, and just heating through on the day (just on a baking tray), may make it easier to prep, freeze, and also to serve as already portioned up.
I would do at least 1 roast potato for everyone. Maybe 2. But I would also do a large pot of mashed potato, or else a big dish of potato stuffing (basically, herby mashed potato then baked in the oven) for anyone who wants more potato than just 1.
Make cauliflower cheese ahead of time - cutting the cauliflower into florets so easier to cook/reheat, and to serve (and less space needed to freeze if you wanted to really prep ahead of time).
Also, make the gravy ahead of time, or at least the stock, and freeze that.
Starters, either a large pot of soup (if you can get hold of a catering or stock pot from somewhere) or something cold (and plated up ahead of time if possible - or at least all the bits prepped to let someone plate it at the table while others work on mains in kitchen) - smoked salmon with capers and cherry tomatoes and shredded lettuce and lemon wedges and brown bread, or prawn cocktail (similar accompaniments without the capers/bread) etc. Or a terrine that you have already sliced.
A large pot will be invaluable if you can get one - ask friends, local scout group, church hall etc could you borrow 1/2. For boiling potatoes, making stock, making/heating soup etc.
Try to maximize dishes in the oven - trays that fit alongside each other, or rectangular casserole dishes to roast veg/potatoes/stuffing etc. Or the biggest trays you have to fill the whole shelf.
If you were to steam/boil cauliflower (on the day or ahead of time), and heat the cheese sauce in a pot, it could just be browned under the grill to reduce pressure on the oven.
For 30, unless you already have the crockery/cutlery/glasses yourself, I really would think about hiring for the day. It really is not that expensive and makes it look so much better all matching even if plain. And you can make the table look more luxurious with placemats/napkins/crackers/flowers/candles etc. You can probably also get serving dishes and platters to make life easier as well, and maybe even extra salt and pepper sets, jugs for water, cups and saucers, milk jugs and sugar bowls etc.
And you will probably need things like salt and pepper, butter, water, gravy, milk and sugar, etc for about every 6 people along the table so no one is stretching too far. And things like plates of bread, extra veg on the table, plates of mince pies or chocolates at the end of the meal etc.
I'd definitely try and have cold desserts as well unless you can do something like trays of a pudding to bake while you eat main course (if you can set the oven to turn off automatically, so much the better). Sticky toffee pudding, bread and butter pudding, some kind of crumble - that's the kind I am thinking of, that can be easily portioned from a rectangular dish, but can be made ahead of time so you just slide it into the oven. Or, if you want Christmas pudding, slice it up and heat it in the oven (under foil so it doesn't dry out) with maybe 1 small one to "fire".
We've made a chocolate biscuit cake type "Christmas Pudding" (BBC website has the recipe) before which has gone down very well with children (and lots of adults) but really looks like a proper pudding.
If you think you want to serve ice cream, I would be inclined to do the prep ahead on that too. Take it out to soften a little and scoop it into balls, lay those on a baking tray and re-freeze. Once hard again, they can go into a freezer bag to take up less room. But they are much easier to serve for large groups and can be served straight from the freezer rather than having to remember to take out a tub to soften but not so early it melts.
Sorry this jumps all over the place, it's just a few things as they fall into my brain.