I really like how you outline quitting your job and starting from ground zero in this post.

My condos, the condo association takes care of the grounds.

(d) This section is in addition to, and does not supersede or preempt, any other state or local law requiring the showing of good cause prior to the regulating the grounds for eviction or termination of a tenancy.

We have a local boots on the ground team and contractors but are looking for the full spectrum to increase our capabilities. 

Those extra "banked" losses cover the future taxable income of the rental activity for an extra few years.I do agree with @Michael Plaks that DIY cost segs are on shaky ground with the IRS. 

So, if any of you have some experience in the real estate market in Germany, or merely some ideas, recommendations (relevant books) or leads regarding from where should  I start my journey, I will be grateful to learn from you. 

@Akeim Fin, I am so grateful for you pointing this out. 

Stand your ground.

Obviously having the team on the ground will be the key.

The first is will what you spend on the guest house going to be returned to you when you sell and more importantly will it make you money when you sell.Typically it is less expensive to add on to a home than it is to create a new structure from the ground up.