Part L is about energy efficiency. Thus having a boiler running just to keep itself warm is considered wasteful. If I understand rightly that you are building a new system using a boiler that isn't going to meet the energy efficiency requirements, you'd be in breach anyway, but since you will be paying for the oil, you may as well have effective controls.
Could you explain what you mean and how you would arrange an interlock between the boiler and pumps since there is none when zone valves are used. The interlock exists to prevent pump and boiler powering on if the valve remains shut
'Boiler interlock' is a technical term that basically means that the boiler is not running just to keep itself warm so when there is no call for heat the boiler shuts down. There isn't a specific 'right' way to do this.
Since zone valves incorporate a microswitch that only fires up the boiler/pump when the valve is open (in effect, the zome valve doubles as a relay), you are wrong to state that there is no interlock when zone valves are used. And while it is true that interlock prevents pump and boiler powering on if the valve remains shut, the point is to avoid the boiler running wastefully. Some of the old gravity boilers will happily fire up with no flow whatsoever and sit there just keeping themselves and the chimney warm, provided there is provision for expansion of the water in them, but this isn't the object of running a boiler.
What I can't understand is how you are going to run your pumps independently of one another if the pumps and the boiler are all powered up at the same time and you don't want to use relays. To me, from the way you've explained this, it sounds like you are committed to having both pumps and boiler run at the same time whenever any of your thermostats call for heat.
The other problem is that, in my view, you aren't asking for general advice. Where to connect vent and feed pipes and pump is covered on about a million diffrent websites, but what do the boiler installation instructions require? Also, a lot depends on site conditions and if you are aren't going to get a professional to design this for you, then you are the only one with in-depth knowledge of this.
Two people other than me have given you advice which you have simply disregarded and gone on to say that what you intend to do is completely different. Remember they are giving up their time for free and I suspect they have less time on their hands than I do. That said, I have quotations to write myself
Do let us know how you get on though, it is always interesting to watch these slightly unconventional projects progress. Sometimes they work very well. Mine did!