2004 Toyota 4runner - CEL on, VSC trac off and engine overheat issue

I just bought a 2004 Toyota 4runner SR5 with 156k miles/one owner from a
dealer last week for my teenage son. Since it was one owner and lower
miles and ran fine on highway during test drive and also dealer showed me
an inspection from Toyota dealer I bought it.

He mentioned that sparkplug coils and plugs were changed by local auto
shop.

My son drives it for a week and then I take it one day, the Check Engine
Light, Air Pressure low indicator and VSC Trac and VSC Off were all ON. My
son said previous day they all came on and went away automatically.

I take it to the dealer and while driving saw that the engine temperature was
going up constantly towards the top.

Dealer checks the code with his OBD tool and said it shows spark plug issue
and wants to take it back to the mechanic and got an appointment next
week.

I change the fuel cap and removed the positive battery plug per forum
suggestions, the CEL went away but VSC trac and off comes on when i put
the car in reverse or drive mode. When I start the car both are off by default.

Meanwhile I see the coolant overflow tank low and filled it with coolant and
took it for a 2 mile test drive, still heat indicator goes up. Next day I see the
coolant level all the way low again.

Looks like I have 2 issues - engine overheat/low coolant and VSC Track
issue. Could bad spark plug issue cause the coolant issue too?