52,000 miles how important is it to drain & refill hybrid coolant, flush regular cooling system, is

None of those are necessary.
Check your maintenance schedule and follow it, using either months miles
The o/m shows how to reset the maintenance minder, and the smell is because they spilled oil all over your engine

 

All this comes from their need to make their next vacation home payment, not from your car's maintenance schedule.

You might want some early fluid replacements, but those should come when you deliberately want such and go ask for it, not from any service writer's up-sell attempts.

Yup, after all that hard sell, they forget the essential element of resetting the maintenance reminder. The simple procedure is in your Owner's Manual, and in multiple threads here.

 

Talk to the service manager. Tell them you'd like to follow the required maintenance schedule, don't want the upsells. See how he/she reacts. If you sense a smoke screen, talk to other dealerships, again the service managers: hopefully some of them are more on the level.

US schedule, converted to graph format, per the Toyota USA warranty and maintenance booklet (you can download pdf of this booklet from Toyota Tech Info):


Note: the inverter coolant in particular, according to Toyota USA, is not due for replacement until 150K miles or 15 years, whichever comes first.

Would you want to share the name of the dealership?

 

Damn, after all that try of robbing and stealing, they try put money on double or nothing.

Posters above added what you should do.
Follow maintenance schedule.