Based on your strategy of buy and hold, I'd certainly focus on the property management side of things as it's the toughest part of the business.My second choice (if you were going to flip at all and manage your own rehabs) would be something construction related.I routinely beat my competition on deals, profits, etc strictly because I'm a licensed GC and know the condition and numbers better than they do.  

It's tough when you are trying to be efficient and drive profits. 

I always suggest looking for "pre-boom" cities that are crawling with investors just yet.Try looking at:The Best Types of Markets for Profitable Turnkey PropertiesandWhat to Ask When Working With a Turnkey Provider

As a foreign investor I think you will need to leave 35% of the profits parked with the IRS until tax time - which means you'll have to file some sort of US tax return.

If you're going to be the only member of the LLC, someone forms an LLC mostly for liability protection but if you have more than one partner then it becomes a useful vehicle having an agreement between the members as to how to run the business and split profits and such. 

Profits from real estate come from cash flow, appreciation, and principal reduction. 

Is it worth the money and is knowledge practical enough to pursue development process?

My primary goals is to create some passive income through rental properties, either single or multi family homes, to start building wealth to secure my financial future and stop working full time to have more time to pursue my passions and enjoy life with family and friends. 

Disclose to the end buyer and the agent so that it is transparent that you are buying and reselling to them4. the end buyer should either be buying cash or their closing company know about the option so that there is no issue with underwriting with the buy n resell5. make sure there is no stipulation with the short sale lender that does not allow you to flip, Some have restrictions on the flip and or for % of profit.6.

This doesn't preclude the fact that just because it's generating income doesn't guarantee you'll actually make a profit, of course.I'm also an investor and landlord.