1. Do Polish people like foriegn food ( like Indian, Turkish , Persian)
Turkish wouldn't work, it's associated with kebabs - but Persian would work very well. The only thing that you have to bear in mind is that the food has to be adjusted to the Polish taste - which unfortunately means sacrificing authenticity a bit. I have no idea about Persian cuisine - but expect the need for salt.
2. How much money I need to run this restaurant? about 100 m2 with medium equipments. ( rent or buy)
How long is a piece of string? It's impossible to say - it depends where it's located.
3. What must I do for legal affairs and How can I get legal papers? Whether must I be citizen?
It's not that difficult - you can apply for a visa on the basis of owning a limited company in Poland. Long winded and tedious, but not that difficult.
4. If I need a business partner how can I get her/ him?
If you need someone with experience, that's not a problem - plenty of foreign restaurant owners would help you out. But if you need people to invest money - forget about it.
They don't like to spend so unless you compete directly on prices with polish there is no way to succeed.
Sorry, but that's only true in small towns and villages in backwards parts of Poland. In big cities, people have money to burn - and will happily spend a lot of money on a quality product.
First of all it is impossible to bring real quality stuff from your country like you can in Germany etc.
Anything available anywhere in the EU is by extension available in Poland.