You can connect the new cooler hoses to the radiator before you install it and connection to transmission pipes is easy enough to do from on top. As I say, both times I did it all without going underneath. I would estimate trans fluid loss to be about an eggcup full at most, that's without plugging the hoses at all. If you've got a pre facelift you're lucky enough to have a dipstick so if you do need to top the fluid up it's easy, just remember to use Toyota Type 1V.