Howdy Nick
I would start by reading the applicable municipalities zoning code and doing some measuring of the site. If there is some absurd parking, frontage per unit, or setback requirement for multi-family then you can probably stop there. Also start game planning your exits, if you want to subdivide and sell, lots of cities have minimum development sizes. There are quite a few cities that allow multifamily, but the way they have zoning codes written you have to be doing a pretty big project to comply.
After that if you haven't done ground up development before, the first place you should start is trying to find a local partner that you can bring in. There are a bunch of decision that you will need to be making that have huge effects on the profitability of the venture. 50% of some profit is better than 100% of a loss because of inexperience. And protecting the profitability of the project is solely the job of the developer, attorneys, architects (of which I am one), and civil engineers have other expertise and incentives.
Otherwise, in most of the states where I have worked start with either a civil engineer or an architect. In some east coast states you will also be bringing in a land use attorney pretty early. But the attorney won't have the ability to but the interpretation of the code onto the real life scenario like a design professional will.
Hope that helps, good luck with the project.