need help with designing new system

just asking for a little advice and guidance in a boiler install that i will do in a few weeks. I am a heating professional, work for an HVAC company, and do most of the boiler installs with 1 other technician and an apprentice. the current heating system is a peerless jo 5 with domestic coil and an electric 50 gal water heater piped in parallel. ( dont ask why!) there is a #30 extrol tank serving the system now so i don't "think" it has a particularly large water volume. we estimate the heating load of the house to be about 135K BTUH. the actual fuel consumption points closer to 150K but it is an old house. in either case the jo 5 is oversized and we plan to replace it with a peerless wbv 04 with a hydraulic separator and an 80 gallon indirect water heater wired for priority. there are currently 6 heating zones. 2 are 3/4 copper fin tube and the others are a mixture of cast iron radiators and sun-rad radiators. the supply and return of these zones is 1-1/4 copper and the branches of most of the tees leading to the radiators is 1/2 copper. most of these zones have circulators similar to B+G 100's although i cant tell exactly what they are. they are piped in direct return and reverse return configs and have both regular tees and monoflo tees depending on the radiators they are serving. i also think there may be 2 or 3 kickspace heaters in the kitchen but that hasn't been determined. so my questions are simple. how do i size the header and hydraulic separator? what type of circ do i need on the boiler side of the system? is a 007 big enough? are 1-1/4 steel headers with 1" branches for circs big enough or should i go to 1-1/2? how about the hydraulic separator? the boiler net is about 158k btw. is there anything that i am overlooking? the pics attached are of what's existing and may be helpful. thank you all in advance!