[SwordMage]

I am not sure about a pure diplomat, one that is a level 1 adventurer; however, I think if you can stand getting to level 9 or 10 it should be possible.

I have been able to travel between most or all of the major cities as a level 10 adventuring character with minimal trouble. Once in a while I run into a wandering nasty that I don't see in time and die, but not that often.

Also, as a level 10 character, I could do whatever faction killing I needed to do to make friends in the various cities.

I did notice that, as a crafter, there were certain cities that were hard to gain faction with through crafting alone (Gnome and Dark Elf factioning outposts were too hard to get to at that level so I gave up and killed things). I don't know what factioning options you have as a diplomat.

Level 10 also gets you a horse sooner than you would be able to get to diplomat skill 100 (or so it seems to me).