Hi Maximil -- the first thing I'm going to advise is definitely getting some lube for anal masturbation. The anus and rectum are not self-lubricating so using lube will help avoid any minor tearing in addition to making it more pleasurable. Is this something you think you could get ahold of? If not, we can discuss some options you may have at home.
As for feces, it depends on a few things. Firstly, feces is stored in your colon not your rectum. Unless you actively have the urge to poop, there will likely not be excessive amounts in there to get on you. I recommend waiting until after you've had a bowel movement on whatever day the play occurs. However! The rectum make still contain residual feces from past bowel movements. Some of those traces may sometimes show up on a condom/penis/fingers/toys when engaging in anal play. It kind of just comes with the territory of anal masturbation unfortunately.