My question is, being my first investment home, should I bother with hiring some kind of designer to help with the material choices/colors/styles/etc or keep with the contractor and work toward a plan and scope of work that way?

It's a great way to get exposed to the, quite literally, the entire world of designers and service providers without having to look all over for them.

So if that area was 10' x 10' that is 4,000 lbs. of design load. 

Unless we know the cost of your lot, how many units you can fit on it, type of design, etc. and whether or not you'll be handling any of the work or subbing it all out, we cannot have any idea of the costs to build.

Is your field of design in residential or commercial?

Had a couple of design issues from the architect, that caused some delays. 

Yes, I believe they do have a great system in place to reel customers in but are missing actual proof of design and feasibility.

*June 2022: we move out of the main home so it is no longer our permanent residence and we begin to get the home ready to become an Airbnb with several construction projects and lots of design and furnishing.

With the apartment project I have found a lot of design inspiration from projects around Austin, TX.  

If it were me, I'd go back and see what I can fix in terms of design and copy.