Have you considered paying a couple of hundred quid to get your movers to do all the packing for you? It's well worth it. Call your movers up now and have them come take a look and quote. If you don't have any movers, call some up anyway and see how much it would all be.
Do a sweep for rubbish/recycles/charity stuff right away after that, today, to clear out the unnecessary stuff. Don't ever use black binbags for stuff you're keeping! Get at least two colours so you don't toss the good stuff.
The movers can provide boxes for you to pre-pack.
If you're packing into your own boxes, Amazon sell moving boxes far more cheaply than you'd expect - 12x12x18" is good for dense stuff, books and plates, 12x18x24 for everything else. Buy a big roll of bubblewrap (or papery equivalent), a pack of five markers and a roll of "fragile" stickers at the same time.
The kitchen and (one) bathroom pack last. Clothes and active bedding reserve until very late (but do the charity sweep!).
Start packing with the rest of the house shelves and cupboards. Pick a room to nearly stack your boxes (this is why it's worth having uniform sizes!). By the time you've done those you'll be over the anxiety and be able to see the size of the job.
Label every box in fat marker! Side and top. "Lounge 1" "Books A-G" "Meadow's CDs" that sort of thing. Only put Fragile on boxes that really are, tag five sides. Well packed glasses etc aren't very fragile.
It'll be fine!