Any thoughts and advice much appreciated

Use the search box at the top of the forum page ^ to search for terms like "security" and "buddy", "photoshop" and "airbrushed", etc - you'll dig up dozens and dozens of threads started by newbies with similar concerns.

Regarding security, if you've got a safety buddy sorted so that you can phone them at the start of a booking (tell the client with a lovely smile that you just need to go and call your security - do this after he's paid, perhaps while he's in the shower, but do mention it to him so that he knows that A) you aren't calling a bunch of thugs to come in and mug him, and B) have security in place so that if *he's* planning something he'll be put off), then you're pretty much okay.

The biggest factor in security is not even letting clients with disrespectful attitudes come anywhere near you. Judge the way they contact you, whether by phone or email - are they polite? (That's good!) Do they address you by name? (Good!) Do they ask loads of sexual questions? (That's bad!) Do they fail to make a proper request for a specific date, time and duration of booking? (Also bad!)

Take your time, follow your security and booking/confirmation procedures, and you'll be fine.