Fellow investors,Recently quit my W2 job(commercial General Contractor) to pursue full time real estate investing.

The engineer can help with this estimate, but local contractors are the top source for getting this info. 

And boasts 24/7 answering service.Anyone have any other companies that sell custom sized windows for DIYer/ contractors?

Focus on potential profit margins and market trends.Be Local: Understanding micro-markets within these neighborhoods can mean the difference between a good flip and a great one.Network: Partner with investor-friendly agents, contractors, and wholesalers who know how to find and secure off-market deals.Nashville's real estate market continues to thrive, and these neighborhoods are at the center of the action.

Operations, well, you need a PM/Sup, you need a bookkeeper, you need a good contractor, and you need an assistant to manage other stuff.

You will still have an electric bill even if tenants pay their own unit.

If you are looking at properties in need of renovation, they want you to know your costs up front and many will be as-is purchases with the expectation that you aren't requesting repairs and your costs are confirmed.Depending on your state, but likely in all states, you have an inspection contingency in the contract, but what you will learn is that you will be competing against seasoned investors and contractors who know their numbers and houses so make better as-is offers.

I'm a radon mitigation contractor who's also certified for testing. 

@Miki SheinaizenI recommend finding local meetups to attend. https://www.biggerpockets.com/forums/521I have found all of my best connections at local meetups.For your BRRRR strategy, partnering with a local property manager and connecting with contractors early on can help streamline your rehab process, especially if you’re not local.

Personal Videos - Sending personal videos to your client whether that'd be congratulating them on getting under contract or getting to closing is a great way to connect.