Great to hear you decided on the most thrilling activity....!
To answer your questions, I personally indeed think it is worth to take a stool/chair with. I bought the green Leisure-Quip one from Outdoor warehouse, with a backrest. Weights 1.1 kg's and I think it's definately worth it. Although one night I struggled with it in soft mud....
I had a backpack of 18kg, + extra tent & stuff (2,5 kg) from my sister, and had no problem. But then again, I'm 21, so it shouldn't. I would advice a backpack of 20% of your body weight, max 17 kg....
The purification: I had tablets and drops with me, yet I only used the tablets, as Donavan (our leading guide) said it unnecessary to use both. The drops contain too much iron, and continuous use is not healthy
Tables were real fine, however, take some Tang or Game flavour with to get rid of the chlorine taste....
You can use a cloth covering the top to prevent solids from entering the bottle, but I didn;t even bother and really had no problem doing so. Just fill up any empty bottle at a 'break' as the chlorine must be in the bottle for 30min before usage
Ndloti: we were specifically instructed to BURN the paper under any circumstances, and I agree it's a very good practice
Shoes: shoes, hiking socks and gaiters are IMHO the most imporatant. Shoes must be worn in, but not too old. The sand along the river is sometimes extensive, and it goes where it shouldn't, and can prove problematic with gaps between the sole and the shoe. Make sure they're good! DO BUY FALKE hiking socks, the thick ones. They might seem too thick, but they are specially designed for hiking, and although they look too 'warm' they are the best, preventing sweating as much as possible. Then gaiters: don't FORGET them, it's just a pleasure to walk with them, and not having to stop every 10 min cleaning shoes from seeds, sands and thorns.
These are the basics, stick to that and ENJOY
I'm Overly OVERLY jealous
Can't wait to go again. Leave the warm clothes at home, you won't need it!