What are the numbers on the digital gauge in your last few pics monitoring? I assume one is your suction line but the other is a mystery. FWIW, the txv is watching your evaporator now. Unless something major changes in that part of the circuit (clog, rupture, ice age, etc) that temp will not change much. Your DX loop is on autopilot now. Whatever you do, don't adjust the txv until you get a solid grip on the consequences.
The other side of the circuit is where the changes will happen. When you add charge, you will have more current draw and more subcooling in the condenser. If your condenser can't keep up, the liquid line temp will rise. This temperature rise represents wasted heating energy. If you remove charge, your current draw and subcooling will drop. If the compressor can't keep up, your discharge temperature will drop and flash gas will form in the liquid line. The txv will compensate by lowering the suction pressure until there is again a solid column of liquid in the line. If the charge is severely low, the txv will hunt as the liquid fills up and drains from the liquid line.
The happy place for this rig is the minimum charge that keeps flash gas out of the liquid line. You will have to experiment to find out how much subcooling your system actually needs to stay stable. Since hydrocarbon refrigerants do not superheat as much as fluorocarbons in the compressor, your discharge temperature will be lower, which is ok if your condenser is effective enough.
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