Vat cst registration in rajasthan & gujarat

Dear Experts,

I would like to know about procedure and cost of VAT and CST registration for a new start-up firm engaged in sales of computer parts in multi-states via online and offline stores.

Please also provide details of both states - Gujarat & Rajasthan. Which one is preferrable?

Also provide me the minimum exemption amount and is it MUST to register for the same before crossing this limit to print VALID invoice to the customers?

Regards,