I'll throw in my two cents worth......simple alignment is done my measuring from a single point at the tounge to the end of each front axle, the distance should be within 1/8" to 1/4" to be sure the trailer is "square". Someone my chime in and have a better way to do this.
As far as tires, if you go to buy them and they offer a four ply and a six ply rated....spend the extra and buy the six ply. I'm not positive on the 13" tires what they offer in rating. I actually think they go by C, D and E rating. Herer's what I'll probably get
http://www.sturdybuiltonline.com/ST2...city_p_77.html
Doing some looking for you, I did see they sell a 13" "D" rated.
http://www.sturdybuiltonline.com/ST1...ity_p_120.html