Tube size will depend on what size tire you have fitted. Obviously, diameter-wise, you're going to want 26".
As far as pedals and shoes go, they're a HIGHLY personal thing. About the only thing I seem to find people in agreement on is that you want more platform than not - go for the one-sided pedals. You'll get a recommendation for every different kind here, so what you really need to do is find you needs and try to find some way to try them out. The big kicker: You're going to take your rites (fall on your side). Get the shoes and pedals and take the rites BEFORE starting out on a journey.
That said, I have SPD-SLs and SPDs. I started with the SPD-SLs on my road bike and have SPDs on my Instigator/Xtracycle. My advice is to go with the SPD-SLs and get a pair of sandals or something else light that you're comfy in for off-bike. To me, they feel MUCH more reassuring - clipping in is more definite than the SPDs AND you get a nice loud *CLACK* to let you know you're in; clipping out is a bit more difficult than SPDs. SPDs are more walkable by a long shot, but they offer a somewhat more difficult clip-in (in my experience) and only a little *click* in comparison with the SPD-SLs.
Shimano offers mountain versions of SPD pedals and road versions of both SPD and SPD-SL pedals.