I feel like the marketing part is too much (and very expensive), and it is easier to start on a smaller scale.

Starting out, I would like to focus on small multifamily (2-4 units) and then scale into larger investments. 

I know how to get fantastically accurate estimates for simple single-family deals but was wondering if anyone had advice on where to start for running numbers for 50+ unit deals.Also, if anyone has any advice on helpful systems and technology - or for managing larger scale real estate businesses to be a valuable partner, I'd gladly listen. 

I would say you are already a little out ahead of your skis because you are talking about growing and scaling without even understanding the partnership and real estate portion of your prospective business.

Doing anything at scale would likely take an act of congress, decades of litigation and environmental reviews, multiple huge overlapping federal bureaucracies working together, not to mention much of the available federal land is not useful for building housing on as it's in remote areas far from jobs with no water and sewer access, roads or infrastructure... so easier said than done. 

Obviously, multifamily has so many more advantages than a Single family home, but can have more barriers to entry.I would start by learning the business, learning how to syndicate and use seller financing, and then focus on two things if you want to invest in multifamily: Sourcing capital and sourcing deals.More units allows you to hire staff and create some economies of scale.

Is there an app that will layout a small scale development?

Leveraging tax benefits like depreciation to scale your portfolio, combined with smart 1031 exchanges, helps you compound your investments.

When it comes to financing, especially for repeat BRRRR deals, it’s important to work with lenders who understand the strategy and can help you scale. 

Always include pillow and mattress protectors; if you plan on scaling it, always have at least 3 sets of sheets/pillowcases.