I also use the Love honey beginner set, and you can also use it with bigger dildos as long as they have a suction cup base.
I always start with rimming and prostate massage to "warm them up" and I always start with the smallest dildo first, then try a larger one if they request.
What you need to consider is that a dildo gives you no physical feedback - so if you're accidentally hurting them, you're not going to feel physical resistance in the same way that you would using your finger. So it's really important to keep checking they're okay, and I always explain this and say they MUST tell me if it becomes uncomfortable. An anus is a lot less resilient than a vagina and it's easy to accidentally cause someone a lot of pain.
Always use a condom on the dildo, and obviously wash them (sterilise them if possible) between clients. Regarding lube, you might want to buy one that's specifically for anal - it's more of a vaseline type consistency and lasts much longer.
There can be a bit of poo from time to time, usually when withdrawing. I have learned to simultaneously roll the condom up the dildo whilst pulling out, which takes care of most stuff (a skill my careers officer at school never made me aware of!) But basically - with any anal stuff, a bit of poo now and then is the price of admission, so if you feel completely grossed out by it, this may not be the service you want to offer!