Sorry it took me a while to reply, this weekend has been crazy.
First of all, when i do look for pictures, i just use search engines such as google, yahoo, alta vista, etc and click the image tab then name of celebrity and search. Personally I like really large pictures that you can shrink to a page cause that works better than small pics enlarging at least for me anyway.
As far as envelopes, i like 10 x 13. they're generally big enough to hold anysize pictures. With the SASE, i usually fold it in half and stick it inside the other with the letter and if i chose to a picture.
As far as how much it costs to send out, it depends. I don't want to give a definate answer becuase mine though generally the same does change every once in a while. I suggest not sealing the envelope the first several times and see abotu how much the letter, photo, and SASE costs together on the outside and then put simialr amount on hte sase. That's what i did when i first started.
I hope that answered questions and made sense. I've not been home long as i have just got off work and its almost midnight here.
Edit: Also, i always had in colored sharpie Photo Encolsed Please don't Bend on both front and back of the sase. The outer one also if i happen to be sending photos.