So, I've accepted a position with another company and am facing the first health insurance change for me since 2011. A lot has changed since then - ACA is full throttle, I have dependents , etc. I'm trying to think this through and make sure I have a correct understanding. So, current job will insure me through the end of Feb. New job will allow me to start on their insurance May 1. Based on my reading of ACA and tax law, I am allowed to have one short-term coverage gap in 2018. Obviously, the mandate goes away completely in 2019, but that is not the case this year. I insure myself and our kids; my wife has her own policy through work. We have no known issues; i.e. no known care to maintain during this transition.

What is the best course of action? Do I wait, and only declare COBRA if something happens (Is this still an acceptable practice)? Do we all surf over to my wife's plan for 60 days and pay the insane premium for family coverage; her plan is expensive for non-employees. I'm trying not to miss something. I have the funds to pay for kids getting sick, but I want to insure I am not missing something if something really bad happens during this interim period.

you normally have 60 days to " declare". Since you only have to wait for 60 days for you knew insurance to pick up I would simply wait, " declare" COBRA if something actually happens during that 60 days and then , if nothing happens, let it simply expire.
Everyone does it, very common.

If the penalty for not having coverage is reduced to $0 when filing tax returns in 2019, then doesn't that mean there is no penalty for coverage gaps or non-coverage in 2018?

I had a similar situation a couple of years ago. In my case, we went without insurance for 4 months. I went ahead and paid into COBRA for two of those months...then let the other two slide as I knew I had a job lined up. That said, I would have paid for the other two months had something catastrophic occurred.

As expensive as COBRA was/is....it was less than going onto the market. The best option at that time was $2100 per month with a $10,000 deductible.

The penalty for 2018 non coverage is applied when you file in 2019. There is no penalty for not having insurance during 2019, so nothing will be collected when you file that return in 2020.

You do get a gap of up to 3 months, so the one month you wont have coverage won't trigger a tax return penalty.