So I am far from being an expert due to me having only a year of experience with The Dark Eye but I can understand the confusion because the Almanac is trying it's best to gather the massive amounts of information that is existing about certain areas and does at best a decent job because it leaves you with more questions open than answered.
I will try to answer your questions as far as I understand it.
Tobimora seems to be a river.
Transysilia is indeed a region. Within lies the demoncity Yol-Ghurmak which is the current (1040BF) capital of the shadowlands, before the invasion she was known as Ysilia.
Agrimoth is one of the Archdemons, direct opponent to Ingerimm (?, the god of craftsmanship and fire. I am not sure about some of the names in English because i do not own the English books, I hope it makes sense for you!)
Oldtoll doesn't ring any bells... I'm sorry.
About the Achaz: These lizards aren't even playable in the current German Version. Maybe with future publications. In Aventurian Bestiary II there are detailed stats about these and also some text but nothing about them being playable.
It has to do with them being very scarce outside of their home swamps and not being well recieved but if you want to play them go ahead and do it! You should make it your story and your world! If you want i could give you the exact stats published in the Bestiary II because i think it has not yet been published in English.
My advice would be to take the available material and build your own Aventuria to which you can add later on if more information becomes available. It's the same for us here in Germany. Except we have some old, hard to come by (and expensive) books, and a nice active community! All of which will take time to appear in the US but i believe you'll get there!