how much do I owe for capital gains for fed and state?

When the taxpayers demolished their existing principal residence, built a new home on the land, and sold it before ever occupying it, the Tax Court ruled the gain resulting from the sale of the never-occupied home did not qualify for exclusion under IRC Sec. 121 (Court case: Gates).

Also, this home along with my other rental is depreciated, that means my real estate company, on paper nets zero dollars..... so unto $80,700 worth of stock market capital gains and dividends - are taxed at a 0% rate.  

After renting out my old home for almost 6 years, I am considering selling it now and curious about capital gain taxes as the house is now worth about $450,000.

(3) if we were to pull the trigger on this, we would likely want to do a Section 121 to preserve our equity gains, as much as possible, and pour it back towards the downpayment of the multi-family.

I see a great one in the mirror behind my set of free weights.

You've got a great situation in that you can sell your primary residence side and take the gain tax free. 

That would kill solar heat gain from windows.But if you haven't switched the vents for summer, yeah, that's normal. 

I know a decent amount of people who will flip condos, so maybe you could find something that needs work and fix it up before you move = instant equity, then sell after living there for two years and don't pay any capital gains tax.Happy to connect you with some good people if this is something that you really want to do.

We were told by our architect that we could legally build out our basement which is a MASSIVE financial gain and the best part is that our foundation guy quoted us $20k to dig out and pour the slab now putting the foundation bill at $130k.