There are a few good options to get started with adult sites on free hosting that are worth the effort. If you want to start on the free hosts and work your way up to self hosted sites as profits increase, tube sites are a good option.
Easyxsites dot com gives you both blog and tube options and you can use either a subdomain or your own domain. You have a wide range of options for monetizing your sites with your choice of ad networks and it integrates with Plugrush for both paid ads and trades.
Pimproll has a hosted tube option (hostedtube dot com) that is pretty user friendly and you can have a nice looking site on your domain up and running very quickly. You can customize your layout, color schemes, niche content and more. You are limited to the ads they place on your site to earn money but they do a pretty decent job with the ad choices.
Tumblr is a good option for adult content just make sure you set the NSFW option or you will get banned very quickly. There are a lot of tutorials online for automating Tumblr blogs that work great for generating good targeted traffic just don't go overboard or you will be banned for spam. Ifttt dot com and or a good tumblr bot will help a lot but you can start out manually and work your way up. There are a few good Tumblr bots out there and I've been using Rootjazz's tumbling jazz for a couple years and they just keep rolling with new features and they keep up with Tumblr changes as they happen.
For ads there are loads of options. Here are some that I've had good luck with. A word of caution, use redirects with caution. Plugrush has a mobile re-direct option that seemed like a good idea and Google spanked me pretty good for sneaky re-directs so I disable all redirect options at this point.
juicyads dot com
plugrush dot com
plugs dot co
crakrevenue dot com
smartxtrade dot com
smartxads dot com
As others have pointed out, you have the potential to lose your content and traffic if the free host goes away but some of the free options seem pretty solid and should be around for a long time. I have seen a lot of free Wordpress multisites come and go and some are more stable than others so I do use those as well. A Google search for free adult Wordpress hosting will help find those. Pornlog dot co and ratedxblogs dot com are 2 that I've been using for a while and have no complaints. Support is limited but they have some video tutorials that can help with the basics.
Good luck and make sure you use only legal content and no spam. Tag all sites as RTA (Restricted to adults) and add a 18 U.S.C. 2257 where needed.