I'm not sure about the tires.. Slightly over inflating them will keep sidewall flex down and tire temp down as a result.
On the oil I use 5w-30 until the motor starts making constant ticking noises. (Usually up around 50-70k miles) Higher milage and/or wear and I'll switch over to a 10w-30 And if a motor is still clanging on 10w-30 I'll go to stright 30weight.
Stay away from the 40 weights. That is pretty thick stuff and the clearances on most engines produced over the last 20 years really is not made for it. Most suseptable are OHC engines. (the lifters over pump and can hold the valves open)
For a trip like your going on, I'd flush the radiator out. Both external and internal. Refill, check the tires and over inflate by about 3-5 psi. Just check the rest of the fluids and have fun.
He who is enslaved to the compass is free to sail the seas