The more I read it sounds like you are going to install the new boiler and rads? It's tricky to install and not as easy as you might think.
I am planning to perform as much of the equipment install as I feel appropriate. I will buy the boiler, manifolds, air separator, expansion tank, backflow preventor, circulators, hose bib/boiler drains and install them adjacent to the wall on which my NGas manifold is mounted. I will buy the PEX and run them from the manifold circulators to where the rads will be mounted.
I have a licensed NGas tech lined up to do the gas hook up to the boiler, and a plumber lined up to perform all copper connections required between components.
I can appreciate the complexities involved and that is the reason I have and continue to spend a great deal of time working out all the details unique to our house. I have extensive experience installing and testing equipment for a profession, in addition to spending several years as a quality auditor that has made me quite anal that equipment be installed properly, albeit not in the plumbing field. So I do feel mechanically confident to perform the equipment installation detailed above with little trouble.
Incorrect install will void any warranty
I have read online about enough instances in which people have had equipment, generally the newer mod con boilers, incorrectly installed by a "licensed" HVAC tech. So although I readily admit such occurrences are surely not common, the fact they do occur suggests that work performed by "licensed" HVAC tech does not necessarily guarantee a proper installation.
I hope that by having a licensed gas tech perform the gas hook up and tests, and a plumber perform the copper work in and around the boiler that the warranty requirements will be satisfied. If not, I have come to terms with the fact my boiler may well not be covered by warranty. But I have never based any buying decision on the guarantee of a warranty, since I know getting warranty work done often times is akin to pulling teeth. So if I do in fact void the boiler warranty in the process of doing what I feel will be my own meticulous work, then "c'est la vie."