@Eric Elmquist
I am basically in your exact situation right now minus the kids. I took out a HELOC on my primary residence at 3.25% and my payments are interest only. Think about that, you can borrow $100k and only pay about $270/month. That is a huge advantage over other lenders in that they will be paying upwards of 15% on borrowed money from private lenders and hard money lenders. I would give you the same advice that went through my brain. Think about what your monthly payments will be with everything considered. Will your regular income be enough to take care of that? If your answer is yes, then I think a HELOC is a pretty low-risk entry point. Other than cash in the bank, I don't think you could be in any better of a position to start investing.
As for the 400k flip in your area, I know it may look appealing but if you are going to make a 400k house look like a 1.2M house that is going to be a massssssssive scope of work. If it is your first one I would proceed very cautiously or even partner with someone who is much much more experienced to help get your foot in the door if you know of someone you trust. There's no shame in starting small to get your bearings straight but going straight for the home run may be a little bit over zealous. Whatever you decide, you are in great shape to begin your investing career for sure. Good luck to you!