Modern boilers either work or they don't, there is no setting up, they work out of the box.
Yes you need a small amount of know how, ie, don't connect the water to the gas inlet because water doesn't burn. There's that many failsafe systems built in that there's zero chance of anything going wrong.
It's not illegal to work on gas in your own home, the rule is the person needs to be "competent", I am, it's been in 4 years without a problem, and the one it replaced had been in 12 years and I fitted that too.