Methodical .
Room by room - even cupboard by cupboard.
Only pull out what you will sort in an hour (MAX) - preferably shelf by shelf rather than a whole cupboard. Take 10 minutes rest (have a drink of water/cup of tea). Go back in again if you have time to continue, otherwise leave that room neat until next opportunity.
Yes, agree the range of bags/boxes. If you won't use items before moving, perhaps wrapping and putting into boxes for the move as you go would be useful, especially if you have any space you can stack up boxes as they get filled. CLEARLY LABEL all boxes - contents and where they belong in new house (you may have boxes from all rooms ending up in that stack).
If it's broken - unless you KNOW you will fix it and use it again - THROW it out/recycle.
Clothes you haven't worn for 5 years or more - recycle, charity shop, consignment shop if they might be worth something.
Linen cupboard with 17 sets of multicoloured (non-matching) sheets, 14 duvet sets, 52 bath towels (varying colours and states of repair) and 41 hand towels. THink of your family size and normal needs. Pick the best sets, put together in sets (sheets, pillowcases, duvet cover) and keep 3 for each bed (1 to wear, 1 in wash, 1 for cupboard). Maybe 1 more if you really want. A few more towels is probably useful but throw out/recycle/charity shop any that are threadbare, colours you no longer use, single towels that don't have a full matching set....keep the ones that are in good condition, particularly ones that match, but keep enough for your general needs.
Also have a look at the odd socks pile while in the linen cupboard, and other things like table cloths, doilies and other sundries.
Book cases. Do you still love everything on there? Would schools use some, or old folks homes, as well as charity shops? The same for music, dvds, videos etc.
Crockery cupboards - Great Aunt Julia's (*name changed to protect poor innocent Great Aunt Meg) antique teaset is lovely, but does it ever come out and used? How often do you use the snail eating forks? Do you need 2 sets of candlesticks or all 15 sets lurking there? What pots do you use every single day, and what pots lurk in the cupboard never used (although, if you use the fish kettle once every single summer for the massive family get-together, and there is a big garden for the same in the new house, maybe that's worth keeping!!).
eBay always seems a hassle to me. Maybe its worth it. But I'd be more inclined to offer things on freecycle, gumtree and similar locally, or put an ad in the "buy and sell" for people to collect (whether for free or buying it from you).
Definitely start early though, as it will result in a lot of rubbish, a good few trips to charity shops and other places that will take useful donations (old folks homes, shelters for homeless or abused women, playschemes for old toys in good nick....all sorts). And probably a need for lots of boxes as you get ahead on actually packing up for the move.