The important issue about cold start protection:
In the beginning, you have something on the order of 500-1000lbs water-equivalent thermal mass of radiator-iron & water at about 65-68F. Can't estimate the real thermal mass without a better description of the radiator and plumbing sizes, but we'll run with 1000lbs for now. It might be as little as half that, but it might be more. If this was originally a gravity-feed coal fired system with 4"-6" plumbing it's going to be a lot MORE than 1000 lbs.
With 60,000 BTU/hr of boiler output, that's (60K/60 minutes=) 1000 BTU/minute, which is plenty for heating up just the boiler from 65F to 110F in short time- a few 10s of seconds probably less than two minutes. But to raise the 1000 lbs of system mass the 40F degrees from 70F to 110F takes (1000 lbs x 40F =) 40,000 BTU, and at 1000 BTU/minute that's a 40 minute burn at sub-110F return water, ignoring for the moment the heat being given up from the radiators to the room. When it's only 45-50F out you'll have a real heat load, but that load is a fraction of what it is at +15F, and it's quite likely that the radiators will emit sufficient heat to satisfy the thermostat without the radiators themselves reaching 110F, which means the return water will be under 110F, and damaging to the boiler.
This is a standard problem with multiple solution approaches, boiler bypass and radiation bypass loops being tried & true standbys. One variation of radiation bypass looks like this:
In this configuration the system pump is pumping toward the bypass loop. A ball valve located where the valve marked "differential pressure bypass valve" is enough, since yours is a one-zone radiation system, and the flow isn't changing. Closing the ball valve would mean 100% of the pumped volume is going toward the radiators, and 100% of the return water entering the boiler is coming from said radiators. If you crack open the ball valve a bit boiler output water is mixes in with that cool return water, raising the temp of the water entering the boiler. Open it up more, the temp of the water entering the boiler rises. The size of the plumbing on that branch loop needs to be substantial but it really depends on he pumping head of the entire system. A 1" diameter bypass branch might cut it, but maybe not ona super low-head system. A real hydronic designer would do the math on the system's pumping head and the pump volume, etc, but most boiler installers would go with whatever worked the last time. A 1.5" bypass plumbing would likely be more than enough, but wide open you may get almost no flow to the radiation- it has to be dialed so that even with a large slug of cool water in the system the temp at the return port on the boiler stabilizes above 110F in the first 5 minutes or so.
Rather than a ball valve (=cheap) this can be implemented with a thermostatic mixing valve (= less cheap) at the intersection of the radiation return and bypass branch and often is, if higher temps are required on the radiation on design day, but I'm going to presume based on just a WAG that you'll never need to hit even as high as 140F at the rads. With the flow split a fixed 50/50 between radiation and bypass at a 70F cold start you'll get your 110F water with the boiler output at 150F you'd have, a sane, comfortable 40F delta-T on the boiler, and as the system temp rises that delta-T will vary a bit as the delta-T across the radiation first shrinks to something like 20-30F with higher temp return water. When the radiation is returning 120F water and the boiler output creeps up the delta-T on the boiler will shrink a bit too. Getting the pump sizing right so this all works, delivers the heat while keeping the delta-T on the boiler under 50F (the likely max operating limit- didn't look it up) under all circumstances is a key part of the design too, but probably not hard to hit. I don't know if that boiler comes with a pump pre-installed, but if it does you may or may not need to swap it depending on your actual system design. (60KBTU/hr with a 40F delta-T is ~3 gpm- you may need it to be more like 4-6gpm starting at a lower delta-T, feeding more boiler of the boiler output back in the bypass to achieve your 110F+ cold start.)
Dead-cold system starts will happen multiple times per year, and tepid-starts will be the norm during the shoulder season. If you tweak the bypass flow such that the mix of return water and boiler output is above 110F a few minutes into a cold start, it'll be above 110F pretty much all the time, and you won't destroy the boiler. With most gas boilers you'd want to set that to 130F+, but the internal plumbing on the ESC takes care of it from 110F & up.
But getting it there is up to the system designer- if that's going to be YOU, it's time to start reading up on it. These tend to not be design-by-web-forum kinds of projects. You have pretty good idea of the heat load, and if you measure up your radiation you'll be able to get a pretty good idea of what your max water temps on the system need to be, and how you need to design the flows to meet all boundary conditions. It doesn't have to be modeled to the n-th degree to work, but it takes more than a coupla napkins and a crayon to get there, and it will take tweaking & measuring while commissioning the system to ensure you don't run into condensation trouble.
If you're plumbing it in yourself it doesn't hurt to add some thermometers on both the output and return ports to the boiler. Otherwise using a wrap of hockey tape on the bit of plumbing where you want to know the temp for spot-checking with an infra-red thermometer makes it easy-it'll be accurate enough for your purposes.
Unless you have two thermostats and two pumps, the adjustable valves you have are there for adjusting the flow to balance the temperatures between what you're calling "zones". In general you'd want one to be wide open, the other throttled back just enough that the temperatures in the different parts of the house served by the two radiator loops track reasonable.