Setting up a company and tax applicability under some circumstanc

I am working as service class and taxpayer. I have my website. Case 1: its my website and I sell products online Case 2 : vendors come on my website and they sell their products. 2(a) : I take commission from vendors 2(b) : I do NOT take commission from vendors Case 3 : I have links on my website and people visit my site and are redirected to the vendor site. There is a possibility that user that is being redirected purchases/NOT purchases the products from vendors website. 3(a) : I take commission from vendors 3(b) : I do NOT take commission from vendors Case 4: I invite vendors to come on my website and register themselves. And in lieu of that I take some money from them. Questions : 1. How to set up a company for the above cases? Please share (a) form (b) procedure (c) time (d) money (e ) Authorities to which we have to apply. 2. (a) What is the difference between Sales Tax / VAT / TIN / Service tax. (b) Which all are required by me in above cases? (c) Please share the form of the one(s) that I require and the procedure to apply for these. (d) How much time is required to acquire each of these numbers? (e ) How much Money is required to acquire each of these numbers? 3. Tax is to be paid monthly / quarterly /half yearly / yearly? 4. What are the negative impact of having Sales Tax / VAT / TIN / Service tax number. Case : I pay tax for one month and next 3 months I don’t have sale. Will govt ask questions from me about this?