I hope that you will give aikido a try. The dojos that I have been at take safety and training safely as a prime consideration. Training safely allows for continued and regular practice.
Unfortunately, sometimes there are injuries for a variety of reasons, but thankfully they are not a frequent occurrence.
This post has discussed a lot of those reasons and I wont repeat them in this response.
Having practiced aikido for over 8 years and in different dojos, where you sit in a line is not always an indication of rank or position. One of the dojos I currently train at doesnt use this sort of seating. Its anywhere in the line. Yes some dojos have a very structured and formal seating arrangement. You should be aware that some dojos may not.
I found that introducing yourself to the sensei at the beginning of the class and speaking with the sempais are a useful thing if you're a beginner. I still do this when I visit other dojos as a matter of courtesy and also to make sure that I get to know their dojo protocols and ettiquette.
The dojos that I have been to will give beginners at each class individual attention, especially for the first couple of months or so. Its kind of like an induction about dojo etiquette, basic ukemi including breakfalls, tapping out. IT also allows them to get familiar with the basic techniques such as tenkan, irimi and tai sabaki movements, escapes from grabs, ikkyo, nikkyo, shikko (knee walking) etc. ITs also a way that beginners can train amongst themselves under the watchful eye of sensei and some of the sempais
At one of the dojos that I train and sometimes teach at, we allow beginners to train with selected senior students and sempais. We expect 1st Kyu and Shodans to take a beginner under their wing to show them the ropes and allow them to get the feel of aikido in a safe and non threatening way. IMHO I think that Ueshiba would like to see all people train effective, efficiently and safely in aikido and for those who are more experienced to look after and help those who are just beginning.
Personnally, I look forward to basic technique training with beginners because they allow me to train my sense of control and allow me to practice techniques fully in a way that the techniques work without injuring and putting undue stress on the beginner. I hope that beginners get something out of training with a more experienced person as well.
I think any dojo that welcomes, looks after, nurtures and encourages its beginners and promotes and practices a safe and effective training environment has to a dojo worth attending and staying with. We were all beginners once and everytime I visit a different dojo that practices a different "style" of aikido I am a beginner again. I know I want to continue to improve and practice aikido for many years to come.
All the best for your practice.