Brownstone Renovations... just getting started

We are in contract on a 2000 sf townhouse (*FAR allows 1300 more sf) and looking for ideas/inspiration. The house in great shape, but we’d want to “spruce up” a bit. Things we may/may not do based on time and price: Expand the kitchen Raise basement ceiling Knock out a couple walls to open up space Demo 2nd kitchen and convert to family room Modern fence in back yard Carpentry work on bannisters/railings Add 2nd bathroom on 2nd floor These are TBD based on cost and recommendations *Central air install (no existing ductwork) *Add 3rd floor as MBR suite *Roof deck With these type of general changes, should we start with architect, or can a good GC handle this. Knowing that there is a wide range, any general time/price guidelines for this level of work? Just getting started, all help appreciated. Thanks! Jason