A bunch of questions about founding a start up comany

The whole internet seems to be overflowing with advice for start ups. Experts and industry veterans share a wide range of information on twitter and blogs, at meet-ups and conferences. They tend to focus on marketing, product development, metrics and financing. Much of this information is contradictory (and much of the information regarding finding investors seems sketchily focused on “luring” them in, rather than rightfully gaining their trust.)

For all the abundance — and diversity — of advice for start ups, I have not yet been able to find anything on more practical, immediate problems, particularly facing start ups in Berlin or Germany more broadly.Assuming that I am already running a landing page to catch some early adopters, and giving them access to a functional prototype/alpha for special conditions to test out and develop my product, I still have questions that I’d organize into two main groups: 1. Pre-incorporation logistics and 2. Legal and tax details of the founding process. 

1. Pre-incorporation logistics:

• At what point should I legally found my company? Only once I am certain that my product and business model will work out? Or should I incorporate before I handle any data from businesses, or from private customers?
• If I were to collect data before legally founding my company, how can I legally transfer the prototype and the data to the company?
• In Germany, having an imprint on your website and following data protection laws is very important. Failure to correctly comply can easily lead to notices from lawyers paid by competitors - without a limited liability company, how can I protect myself? 
• How do I handle expenses I incur before officially founding my company? What should I do about them if my plans do not materialize before legally founding? Are there any tax breaks that I can claim from pre-founding investments or expenditures? 
• Can I "hire" any help in advertising/marketing before founding a company?

Assuming I decide to start a German UG company (basically a limited, with some more drawbacks), this leads to another group of questions.

2. Legal and tax details:

• How much collateral beyond the first necessary Euro do I need in reality? Does that have any practical impact on how my company can interact with other companies?
• What other costs can I avoid? I have to pre-pay taxes, but how should I go about making good estimate of what to pay? Should I try to over or underestimate? I can avoid the IHK membership fee at the beginning?
• How should I handle expenses I privately financed before founding, e.g. hosting a landing page, some marketing costs, money spent to research the market and buy publications?
• How much money should I put into the company to keep it solvent, but not have more unused liquidity in it than my personal bank account can't handle? How about adding more money later on, especially when there are multiple founders? How to balance stake vs money put in?
• In case I suspect that my company will be bought at some point, should I have a holding to hold the actual company, e.g. to avoid the early payment of taxes?
• If I plan to have investors, do I need to take any preparations to easily enable parts of the company owned by third parties?
• Should I use the "Musterprotokoll" when founding my company or should I have a custom one made? Should I use a service provider like go-ahead or firma.de to found the company, or  do everything on my own?
• Should I found have a German company, or an English, American, etc. one? Especially in software and SaaS, being some other place may be easier tax- and data protection-wise.

I am aware that a lot of these questions depend on what my specific enterprise will do and I will need to talk to someone professional - but who should I talk to?