Safe way to start my car after not running it for 5 months?

Safest way to start a dangerous car is obviously to have someone else do it. Preferably someone you don’t like. While you stand far, far away. Otherwise, you risk this:

Charging batteries generates hydrogen I think don’t be like me and do it next to the boiler

A recommendation if you don’t use your vehicle very often.

At least once a week, go out and start it and let it idle for like 10 to 15 minutes, then have it driven around the block. Nothing major, just a small drive to keep everything working smoothly. If no one can do the drive, then go up and down your drive way a few times.

If the car is going to set in the sun, you might want to consider some sort of wheel coverings because the sun will (slowly) rot the tires. It’s called sun rot or dry rot.