You should be safe to do a simple tranny 'drain & fill' & replace the drain plug gasket......I wouldn't suggest a complete 'power flush' though.
Throttle body cleaning should be under $100...as far as a full tune up, I'd recommend plugs, wires, air filter, fuel filter & PCV valve. Once that is done, see how the car goes. B)
Any idea what is wrong with the ABS system?