Can't speak for Poser but Daz3d has nice joint integration (click+drag) that makes it pretty easy to pose characters.
If you're just getting your feet wet, look around the torrent search engines for 'daz3d' and/or 'renderotica'. There are some 1-10gb torrents floating around that have huge archives of just about everything that's available publicly. Obviously buy the content if you're going to be setting up a patreon or something, but you shouldnt have to spend thousands of dollars tinkering around with side projects.
Doing guro in 3d is a relatively hard thing in comparison to plain vanilla stuff.
But if you want it free you should use daz3d which is free and has more content than poser. and you just need to register on their website and take it for free. there are plenty of sites with pirated content.
Those 10gb renderotica torrents mentioned earlier are not that good since they are mostly old poser stuff but you can find some useful stuff there.
If you really want to do guro stuff, you will need Zbrush for morphs and photoshop to edit textures everything can be downloaded from torrents