I got interested in Georgian about a year ago. I'd studied a number of languages, but none of them had ejective consonants, ergativity, polypersonal verbs, etc., even though these are all common features globally - they just aren't usually found in European or Asian languages - so I decided to find a language that would have those exact features. There's a whole slew of native american languages that fit the description, but even Navajo, the largest of the native north american languages, only has something like 200,000 speakers and no literary tradition, so unless you happen to be living in a reservation or something, that's just not practical. Then I found Georgian, which has ejectives, polypersonal agreement on verbs, ergativity, etc., so it's pretty much perfect, and with speakers numbering in the millions and a rich literary history, it is both practical and possible to study. And in addition to the features that are common globally, Georgian also has a number of rare or unique phenomena like harmonic clusters and unusually liberal phonotactics.
I have a number of books on Georgian, and my main book is Howard Aronson's Georgian - A Reading Grammar
. I'm only half way through it, but it's quite thorough. What is the German book you found called?
As for the difficulty, well, I think you have to keep in mind that there's a difference between difficulty and complexity. I would say that Georgian is the most complex language I've ever encountered, but I would also say that something like Japanese, even though it has a much simpler morphology, is waaaay more difficult for someone whose native language belongs to e.g., the Germanic family or the Romance family. The Georgian future screeve has an intricate formation, but at least Georgian has one - Japanese just has a non-past form, and that's infinitely more annoying IMO.
Because I'm only half way through a beginner's textbook, I don't think I could really help anyone with their Georgian, but I wish you luck and welcome you to the forum. This place is almost as quiet as the Berber forum, so we need some more posters