What size tire iron do I need & other questions...

I just use my tow vehicle's jack for changing the tire(s) on my TT. I tried it at home to make sure it fit and works. I bought a socket and socket wrench that fits the lugs on my TT wheels - I prefer using a socket wrench rather than a tire iron when I can. You do need a larger, heavy duty socket wrench.

Just make sure that whatever you do, practice at home! So that if (hopefully only if!) you need to change a trailer tire while on a trip, it won't be the first time you use all the equipment.