You will find many links within the advice and photos pages. In general terms we can make the following suggestions for websites / links you might like to use in advance of your journey.
The Exodus TYU route
was the option we chose (but see the relevant advice page for other options)
The Foreign Office travel advice web page can allay any (unnecessary?) anxieties about travel in a sub-Saharan country, with the proviso that their advice will always err on the extreme caution side!!!
For general reference guides we used the Rough Guide to Tanzania and the Lonely Planet's Watching Wildlife - East Africa books. For a comprehensive list of books about varied aspects of Tanzania look at the Ranker website.
In an organised group you do not really need maps. However, at the end of our trip, we bought at KIA airport several illustrated wall maps of the national parks and of Kilimanjaro which have been excellent souvenirs. If you wish to purchase maps in advance contact the Map Shop in Upton-upon-Severn.