Hi,my advice to you is take that opportunity and do Ausbildung if you believe your FUTURE is in Germany. Also after your ausbildung you will be able to stand on your feet no matter what country or continent you will be living in FUTURE.
1.Check if is possible to get all documents.
2.A level of Education you had before you came to Germany.
-Did you finished a primary school(In other countries 7yrs)
-Did you finished a secondary school(In other countries 4yrs)
-High School Education level(2yrs in some countries)
-Do you have Dipl/Adv.Diploma e.t.c
Your Education backgroung will play a big part in School and at Work. Here I am not talking about how good or bad your German is not at all.Dealing with homework,test,exams,calculations,stress etc. DISCIPLINE also is a key at all time(at work,school,home etc.)
3.Know what kind of Ausbildung you want to go for. Make your decision dont let other people choose for you. When you know what are you after,then find people who you know their doing that Ausbildung and have a chat with them, if possible check what their doing in School.I mean open their books,check the Topics and see on your own eyes whats going on. If you can not find one go to Berufschule and ask Teachers,they will be happy to help you. Also JOBMESSE if is possible but the problem of Jobmesse in this country you will not be able to get a clear picture of what your about to face in school. May be its work for Germany kids but many brothers and sisters ending droping from Ausbildung after few months if not weeks.
4.Language should not be a your obstacle. If you will be able to understand 30% of teaching then get home and add 20% to reach 50% for the first year.That will be enough to take you next level. If you will be able to get above 50% that will be greater. 2 year you can reach 70% or high. That means when you reach 3rd Year you be capable to go for your FINAL EXAMS without a doubt.
5.Deportation ban is necessary at this stage I dont know. But as longer your Asyl case is still running your safe. Try to read what LAW say about DULDUNG HOLDERS after finishing their Ausbildung. Their is certain documents you have to bring before the authorities can decide on a case.
6.What will happen after Ausbildung nobody knows because it will depend on what LAWS says,which State your living,who is dealing with your case at Landrsamt,political vacuum and so on.
7.About Tax issue I dont know but on my opinion it will make more sense and make a Jugde think twice if not more time to decide if your doing your Ausbildung than WORKING if your to be taken to court regarding your Asyl case.I hope you got what I mean.
8.Ausbildung will help you on your retirement(Financialy). I dont want to go dip on this.
I hope this will help,all the best