remember turndown is a ratio of total capacity and the other variable to get better control when working with multiple boilers in a single system is to vary the size of boiler as well. I.E., have a couple larger boilers to run steady load and smaller ones to trim.
Spirax sarco is always a good choice for components and I personally really like their Hook ups book:
https://www.amazon.com/DESIGN-FLUID-SYSTEMS-HOOK-UPS-Spirax/dp/B000NQ5U42
great steam tables and recommended setups for traps and condensate returns for different types of loads.
the Miura is technically more of a steam generator vs boiler. there are many types to research. look up firetube vs water tube vs steam generator. all have pluses and minuses. I have worked with cleaver brooks (firetube), miura (steam generator), vapor power( water tube), and a couple others with good results.
from an engineering standpoint the vapor power watertube is interesting because all the steam creation happens in a expansion tank after the watertube making all your watertube last a really long time and all your blowdown needed collects in that one expansion tank.