It all comes down to your own prefrences and dislikes, waiting time is in no way definate for any actor/ actress. You might wait a week and somone else might wait a month, also there is always a 50% chance of not geting yoyr items back, this is a hoby of risks.

Honestly, there are no definite answers!

You can send whatever size envelopes you like - use the smallest that your items will fit in and check the postage, as large letters cost more than small letters, etc.

You don't have to include your own photo for them to sign, but you'll find that some people don't have anything to send so you'll probably have a higher response rate when you send something. I print them myself, but you'll find other threads with links in the forum.

You can buy US stamps from ebay. The standard stamps are "forever stamps", and there are also "forever global" stamps that will send a standard size letter to the UK (and most of Europe). Of course it costs to send letters to the US! A standard letter is £2.15, but larger letters will cost more.

Response times will vary wildly. I've had some back in a week. I've had some back in 4 years!

No idea about cast cards as I've never written to soap stars!

Another good bit of advice is never send anything that you can't afford to lose. You'll send off a lot of stuff that will never come back in any state! Some places will return items unsigned, but many people will misplace, lose of dispose of your request - it's a fact of this hobby I'm afraid!

Last thing - always check postage on the relevant websites (royal mail, USPS, canada post, etc). I'd advise that you add a few pence or cents to the SSAE too as sometimes your reply will be sent a long time after you send it and postage may have gone up a little.

Good luck!