Tim DO IT. Daft adventures is what young men (and women) are supposed, nay must, do. Years ago some friends of mine went climbing in Scotland in winter in Wellington boots. Some older club members, myself included, were appalled and ready to chew out these young guys for being badly equipped until one of my peers calmly pointed out that that sort of thing is what broke young men do, that we ourselves had done when we were broke young men. The bike touring I do nowadays is chickenfeed compared to the stuff I got up to decades ago. I don't really have any advice re bikes: I once met a young man in Kentucky who had rode an 8 speed Schwinn he'd found in a ditch from LA to there. He couldn't afford ACA maps so he'd done it mainly on freeways. His weather gear was a black plastic garbage bag with holes for head and arms. He was living out of dumpsters.
As your cause is supremely worthwhile but not well known (at least to me) I suggest you travel with placards explaining your charity and make up some little fliers explaining your charity in detail and among other things how donations are handled and kept separate from your own finances (a local Staples might do that for free)
Don't be a Blanche Dubois, you can't rely on the kindness of strangers but you will be thrilled to find how much of it there is out there. Have fun.