From the sounds of it, its slowly eating coolant through the LIM gaskets.
The hard starting is likely a very dirty MAF sensor and Throttle body blade, both of those should be taken off the car and cleaned with the correct cleaner, its a very simple job that should fix that issue.
Also being that, that coolant has 100k miles on it, I'm sure its had a chance to get all sludgy and brown and disrupt coolant flow to the heatercore and preventing you from getting heat at times.
If I was you, I would replace the intake gaskets, back flush the heater core and flush the coolant system, then if you wish switch to green coolant. A flush can be done with a garden hose and some know how.
