While the suggestions you have so far received are correct, there will continue to be bottlenecks regardless of what you do outside.
You are installing an irrigation system that is designed with a 3/4" diameter mainline, which is being supplied by 1/2" piping. Perhaps it will not require a 3/4" supply, but that will depend on how many emitters are to operate at the same time, and the flow rate needed for each.
In addition, since we can't see on the other side of your foundation wall, for all any of us know, there maybe a section of 1/2" PEX line feeding the copper exterior faucet stub, and the interior isolation valve may not be a full bore ball valve but may instead be a 1/2" globe valve that will also be restricting the flow rate.
Although 90 psi static pressure will assist to increase the flow rate through the 1/2" supply line, that pressure is too high for a residential application. City of Toronto typically supply ~60 psi through the municipal system, so assuming your gauge is accurate, this leads me to suspect you are utilizing an alternate water source such as a private well?
Since the supply pressure for residential applications should not exceed 80 psi, perhaps your well pump pressure switch setting is too high or, if water is from another source, your Pressure Regulating Valve maybe set too high or is not regulating pressure properly.
THIS WAS A VERY GOOD POINT
I totally forgot about that valve that I turn off when the cold weather is here
Damn ..that ruined all this work. I am not prepared to change that valve, it requires removing drywall, soldering in a tight space. Maybe I should bite the bullet and do it I am the one who soldered the outside copper female adapter so that worked OK and I also soldered two copper to PEX adapters which are still OK after 1 year so it might not be that bad but replacing that valve and having to remove the drywall around it so I can work and then finish and paint back is going to inflate this project more than I wanted it to.
Tthe 3/4" requirement for the PVC pipe line that feeds the irrigation system is based on what is easily available here in the store
Here you can see t
he initial irrigation design/plan .
However I decided to simplify that to the minimum and use a mix between the in ground and above the ground irrigation system with the plan to upgrade that later to full underground.
Here is a sketch of the new temporary design
With the plumbing design discussed here in this thread (area circled with purple) I thought I would have 3/4" all the way to the manifold.
The plan was to I use impact sprinklers which I do not mind leaving permanently there if I can quick connect them to an underground pipe. With these I could easily cover the two sections of the garden that I need to cover. (see the plans in the link to the irrigation thread).
Considering the needs I could easily cover the areas with impact sprinklers or with oscillating sprinklers
The idea is to permanently build the segment from the water tap to the manifold and from there to test using an old hose that I can cut and use the segments to connect the sprinklers and the manifold quick connect ends. I can test and relocate the sprinklers as I wish, daisy chain them if the pressure allows me to do that and size the system as I go through this experiment.
I think there is still value in building the system as guided in this thread (thanks a lot guys!!) and then later replace that inside valve which is 1/2 most probably and it is a regular valve (one of those with circular handle).