Coolant issue? Internal leak?

[Coaster]

Had the car in the shop not too long ago for IMS/RMS and a few other things. Not sure if that is related or not.

Over spring break I got a P0300 and P0304 code (misfire on cyc 4). Found a few drops of oil under the car while changing the brakes. CEL turned off next time I started the car. I was planning on asking shop to scan at the next oil change. Again, not sure if it's related.

Late last week got a red low coolant warning in the morning. Topped up with a little under 1/2 gal of distilled water. Yesterday I was checking the level after work and think I didn't get the cap on tight. Drove about 35 miles at 80+ on the toll road - no lights or warnings. Just as I pulled into the driveway the red coolant warning came on again and the car barfed on the driveway. Cap was loose as I said.

Let it cool down and topped up with distilled water and drove about 5 miles and got a red low oil pressure warning just as I pulled in the parking lot. Had the boys bring me some oil and distilled water. After sitting about 3 hours, the oil level was fine but the coolant was low again. Topped up again and had my son follow me home. He says white smoke appeared when I started the car. Got a CEL and a yellow "drive to workshop" warning on the drive home.

Haven't seen any water under the car (except when it puked on the driveway). Makes me wonder if I have an internal leak (especially with the white puff of smoke).

Shop says I need a pressure test on the cooling system. Hoping it's not an oil to coolant leak. Thoughts / suggestions?