Just a thought from a life long musician (certified in music ed) who started lessons with an excellent teacher 3 years ago.
As you have observed, the three types of harp are very different. But also, you must take into account that the harp itself is VERY different from all other instruments, and having taught all of them except harp, I can tell you that it is definitely the easiest instrument on which to develop fiendishly bad habits quickly.
If you want the same joy that you have from the harp as you have from other instruments, find a teacher and rent. I didn’t rent first and if I had, I would have purchased my lever harp from the same maker (Thormahlen) but bought the Swan instead of the Serenade.
I am now taking lessons on pedal harp and love it, so no regrets at all about my Serenade, which sounds wonderful.
I have been frustrated along the way because I’ve considered my progress to be slow, but I am getting to the point where there are sonderful pieces within my reach. You are not too old to do the same. There are some very good tutorials out there, but I’d bet that even the people who developed and published them would tell you that teaching yourself is not the same as being taught in the presence of a living teacher.
Do what you love!