It is never good to bring a suction line down to a jet pump. Any high spot in the line will accumulate air, which will get sucked into the pump and cause a lose of prime. Suction to a jet pump should always have a slight uphill grade so that the pump is the high spot in the line.
Also a union like that on the suction side will probably cause a suction leak and loss of prime.
I don't know anyone who is happy with 20/40 pressure, especially if the pump is down in the basement. That pump will only do about 2-4 GPM at 50 PSI, depending on the depth to water in the well. I don't think you will be happy with that pump. I hate when people have a set up like this and complain about the pressure from the pump. Always "wishing" they had good city like pressure. Well it is your pump system, you can have as much pressure as you want. Pressure from a pump system can and should be much better than city water pressure. So don't complain about low pressure from a well or pump system when it is just the pump system you chose that is causing the problem.
With that large a pressure tank and a 20/40 pressure switch, you will only have about 10 PSI upstairs in the house until the pump comes on and increases the pressure to about 30, which is still not good.
With the right pump controlled by a PK1A using a 40/60 switch, you would have a constant 50 PSI at the pump, and good 40 PSI upstairs in the house. I am not sure you will even get wet in the shower with the 20/40 set up you are planning.