Regarding your first bullet point, you do have the option of signing up for ACA in August, because losing your employer coverage in July is a qualifying event that allows you to sign up outside the normal enrollment period in Nov/Dec. You would qualify for subsidies this year based on your income this year. Of course, if your income this year puts you above the ACA subsidy limit of 400% FPL, then you would not receive subsidies. In that case you'd still qualify for ACA coverage, you'd just pay the full price. And if you do this option, you'll also qualify to reenroll (i.e., continue your ACA plan, or switch to a different one) for 2020 in Nov/Dec and receive subsidies in 2020 according to your 2020 income.
Regarding your other two bullets, most ACA plans do not cover care out of network unless it is emergency or urgent care. Emergency or urgent care is usually covered at a lower level than in-network care (so you might have to meet a higher deductible, or have a higher copay or coinsurance for emergency/urgent care). I don't know of any that do cover you fully out of network.