Prefab boiler panel for phased hydronic upgrade

Hi all,
I’m planning a phased upgrade to my home’s hydronic heating system and would appreciate some feedback from the pros here.

Current system

• Older cast iron boiler (Peerless WBV series) with a Carlin EZ-Gas conversion burner
• Two zones today:
  1. “Main House” (mixed cast iron radiators + cast iron baseboard)
  2. “Addition” (cast iron baseboard)
• Each zone has its own circulator (currently Taco 007s) and both zones are pumped on the return
• Near-boiler piping is functional but messy/maze-like from years of modifications (pipe size changes, some dead-end runs, etc.)
• Boiler is basically on/off, 180°F type operation (no mod-con yet)

Phased plan

Eventually I’d like to convert the whole house to radiant floor, but I’m doing this in phases and want to build a clean “backbone” now.

What I want to do now is

• Repipe the near-boiler area cleanly
• Convert the current 2-zone setup into 3 zones (split Main House into Upstairs/Downstairs) while I’m already cutting/repiping
• Keep everything as high-temp water for now (180°F-ish), since I’m not installing radiant yet
• Use copper for the near-boiler “panel” and oxygen-barrier PEX for the distribution runs
• Install a hydraulic separator (I was looking at the Caleffi SEP4) mainly for:
  • hydraulic separation / decoupling boiler flow from system flow
  • air elimination
  • dirt/magnetite separation (I’m sure there’s plenty in the system)
• Stub/valve future ports for radiant so it’s easy to add later

Wiring constraint

Upstairs is tricky to wire for a new thermostat. I currently have central AC with a wired thermostat upstairs (attic air handler). I’m considering using a thermostat setup that can run wired AC in summer and provide a wireless heat call to the basement zone relay in winter.

Prefab panel question

I’m considering buying a prefab “boiler panel” (pumps + control relay, etc.) such as the RHT Trident Boiler Panel type products, and then using a hydraulic separator between the boiler and the panel.

My thinking is:

• prefab panel = clean, tested, professional layout with 3 zone pumps + relay
• separator upstream = hydraulic separation + air/dirt separation + future-proofing
• I can connect my three high-temp radiator zones now and add radiant/mixing later

Questions

1. Is it appropriate to use a prefab “radiant boiler panel” even if I’m NOT installing radiant yet (just high-temp radiator/baseboard zones)?
2. Is it reasonable to place a hydraulic separator (air/dirt) between the boiler and the prefab panel, or is that redundant / incorrect?
3. For a cast iron boiler, anything I should be careful about regarding low return temps / condensation if I add hydraulic separation?
4. Would you recommend pump-per-zone for now (3 ECM pumps), or go straight to one system pump + zone valves?
5. Any “gotchas” with these prefab panels that I should be aware of (pipe sizing, flow limits, serviceability, etc.)?

My father-in-law is a licensed pipefitter, so I will have him help out, but I want to learn what I want before bringing him in.

Thanks in advance — I really appreciate any guidance.