Or can you just factor them in together?

Probably not much if you look up the factors for score it may affect type of credit and length of credit history as well as number of accounts but as long as you don't miss a payment you should be fine.

The taxes does suck, but coming from NYC, it is similar when you factor other carrying costs.

You will definitely want to factor more economic vacancy right now, 12-18 months reserves per current lending requirements, lower LTV  and much lower rent growth, depending on the asset and location, if any at all during this time as we will see more and more rent controls coming out of this situation.

So, if the numbers make sense to you, you need a home to live in, you can afford it no matter what the market does, it offsets what you might currently be spending on rent, or any other such factors, this could be an ideal time for you, personally, to buy.  

If I were in your shoes, I think a factor would be how good a deal you're getting.

That’s not factoring in short sales.

With a local and reliable contractor like myself to hold down costs and schedule to the extent possible, that’ll be the best mitigating factor for the riskiest part (construction) assuming you buy the land at a good price, and have the correct expectation for selling price when it is done. 

I ran the numbers - factoring in the 4 profit centers, I estimated I would recover the 10% penalty, 32% fed tax and state taxes within 3 years.Assuming your 401k had 100k, you would have 53k to invest.

So factor in -6% on your market rents on top of what is sure to be at least a doubling of bad debt, delinquencies, etc...