The boiler is the easy bit.
It is the bit that costs the most money and the bit where "Boiler throwers" do best.
However,
Controls is what makes or breaks a heating system.
Controls is also what will make or break your wallet.
A boiler install is no good if the rest of the plumbing is dirty, old, knackered etc.
Whomever you are getting to put the boiler in, have a good discussion with them and get them to explain what boiler it is and why it suits and what they will do to ensure it mates with your system as good as possible.
Ideally, if you have a friend who is a plumber/hating engineer, or just a nerd, then get them to look at what is being done.
You are forum savvy. there a lots of DIY forums you might sign up to and show them what you are getting into before letting the ink dry.
But, a few quid on controls will be well worth it and in short time as well.