With the free manga, I confess, I have a tendency to just grab anything that sounds like something I might potentially read without giving much thought to my current level of language ability 
. I just read a volume of manga this year that I picked up for free over two years ago. I’m probably pickier than the average person though because I primarily read LGBTQ stuff and won’t read works which strongly center heterosexual romance. So I grab basically anything that has an LGBTQ tag in the freebies thread. I’d say just grab the ones you think look potentially good now and worry about reading them later. You might graduate from very easy manga sooner than you think!
If you’re willing to mess around with installing a new program, there’s also Mokuro (and ChristopherFritz’s BookWalker manga screencapper), which will let you use popup dictionaries and such on manga. Thanks to Mokuro, I’m able to read manga with lots of unknown vocab much, much quicker because I don’t have to do manual lookups. This can make difficult manga much more accessible!
I personally didn’t find manga to be the most helpful learning source for me, so I ended up sort of avoiding it for the first year and a half or so (with the exception of one ABBC book club manga), and only recently have really started to dive into it because I’m able to enjoy it a lot more now that I can read at a decent speed (thanks in part to Mokuro) and can read the manga that I actually want to read. So I effectively skipped almost all of the classic beginner manga, except for Yotsuba, which I’m reading as an upper intermediate learner instead of a beginner because I love the series in English and wanted to read it when I could enjoy it more.