Agreed on the flush vs. drain and fill on the transmission, never do a machine flush on an auto. While it sounds like a great idea, it loosens all sorts of stuff and shoves them into tiny passages that can do more damage than good.
My transmissions had been killed by doing this (Dodge Durango), and one other trans was saved by doing the drain and refill (Honduh Odyssey). It may be slightly more expensive to do it right, but you won't need to worry about a new trans.
And, while I understand you cannot afford to do all the work at once, I would definitely do the trans first. The diffs will survive on 100k+ oil, so long as you aren't drag racing it daily! You will be very unhappy if you blow up the trans because you didn't keep it serviced! Just think of THAT bill when it happens!
Fuel injector service is great, if its really needed. Is it hesitating or running poorly? If it is, try throwing a can of BG 44K into the tank, see if it clears it up. If it does, throw another can in after another 1,000 miles (~4 or 5 fill ups).
If it doesn't help, then do the fuel injector service. Btw, BG 44k is what many dealerships use when they do a "fuel injector service"! I know of a few Toyota dealerships that use BG products for lots of "services"! Hard to find someone that will sell 44K to you though, I get mine off Ebay now, nobody there cares who they sell it to.