Have you read:
Trail Life: Ray Jardine's Lightweight Backpacking by Ray Jardine?
A truly excellent book about hiking the long trails in the US. Not everything is applicable for use in the UK, particularly Scotland, but some is. Using a quilt instead of a sleeping bag, for instance. Tarps instead of tents won't be great for a short trip with midges, but they make a very compelling case for them on the long trails. They are great advocates of sewing your own gear and have enough instructions that even a talent-less bloke like me can make some headway.
Sleeping bag vs quilt. I like my down quilt, I have a Jacks-R-Better from the US, but if I was shopping for another such thing now, I would get one of these:
http://ukhammocks.co.uk/products/ukhammocks-down-tq-winter?variant=1064806648. I have one of his underquilts and the quality is a very good and no messing with shipping, handling and Parcel Force ransoms. After reading the afore mentioned book though, I would probably make a synthetic quilt for the long trek.
From what I can tell, the long hikes in the US drive gear selection quite differently than gear selection for shorter multi-day hikes. A couple of weeks is a reasonably long walk in the UK but will only just be getting started on something like the PCT.
Another vote for J-Cloths. I use one for a wash cloth & as a first stage towel which saves my light Paramo travel towel from having to get too wet. J-Cloths are anti-bacterial, very fast drying and can be easily squeezed out. They don't start smelling like swamp water after a couple of day's in the field, unlike a lot of things. I am not a fan of cotton shemaghs for that reason. Only down-side to J-Cloths is that they lack scrubbing power, so they don't do a great job of scrubbing ones face as clean as you might want. Jury is still out on these new "E-Cloth" cleaning cloths. They certainly scrub well, without soap, but not sure how well they will dry. probably not fast enough, but better than cotton.
Used a shemagh on a canoe trip in the west of Scotland. Never again. Never dried out, stank.
Ditch toilet roll, use pre-packed Kleenex tissues. I know Mors has his methods, but the individual packs are a safer option in our wet climate. Balsam ones burn well, but don't soak up water as well as the standard ones. One packet per day, all purposes, and they won't go to instant mush if you drop them in the wet heather. Just don't leave them as litter. Don't take any form of wet wipe or cloth, they are not biodegradable in the environment, whatever the packaging may say.
I have an Aquapure traveller water bottle,
http://www.purehydration.com/all-products/emergency-aid/aquapure-traveller/
which I like, but it claims to be good for only 350 liters. No batteries to run flat, but if the water is not clear you probably won't get the same one to work for the PCT that you use in the run up to it. Steripen might be better in that regard. Not sure.
Another fan of merino wool and Paramo clothing. There is a paramo seconds shop on e-bay that is worth keeping an eye on, otherwise the gear can be hellish expensive. I have managed to get a lot of mine on sale, but that takes time.
Very best of luck! and don't over-do your training too quick, injuries are all too easy to pick up, and can take a long time to go away.