Two things...
 

I will be traveling to Japan in November. If someone asks me where I am from (Anata no shusshin wa doko desu ka?) I plan on answering:

Watashi ha Shiatoru, Washinton ni sundeimasu.

And if I happen to be complemented on O-hashi or my paltry use of Japanese, I plan on saying:

Iie, mada mada desu! Domo arigato gozaimasu!

Is this correct?

Thank you!

'Watashi ha Shiatoru, Washinton ni sundeimasu.'
→'(Watahi wa,) Washinton (shuu) no, Shiatoru ni sunde (i)masu.'
or '(Watashi wa,) Washinton (shuu) no, Shiatoru kara kimashita.' would be more natural.

'Iie, mada mada desu! Domo arigato gozaimasu!'
→I think it's perfect.

Thank you very much for the good advice! :)