Often it is best to contact an architect to determine a number of questions, the primary being budget.
Having the project designed allows you to provide contractors with stable scope of work that is to be followed and your architect should be able to give you information about your budget and if the budget fits the scope. The architect can provide you guidance to good contractors and provide guidance with assessing bids.
If you do not feel comfortable with an architect then you should determine the scope of work that you can provide to contractors as you probably want more than one estimate, The scope may include permits, drawings that may be required, list of subcontractors to be used by the prospective contractor and the time frame for completion. Ask the contractors what their time frame is like and what other contracts they may be working on at the same time.
Ask the contractor how they plan to protect your property during the construction process. I believe you said you wanted a second floor built on your property, will that require the interior of your home be exposed for any period during the construction?
Good luck with your project!