T1 carries full current to the motors. It needs to be rated accordingly. (Probably a TO-3 PNP general purpose.)
R1 R2 T2 are in the control circuit. They only need to carry small current, enough to turn T1 fully on and fully off.
The relay coil carries several mA, maybe a few tens of mA. Therefore R3 R4 T3 T4 carry small current. Just enough to turn T3 on enough to activate the relay.
From what I've seen reed switches are not rated in any particular manner. I suppose the general idea is to treat them gently in order to lengthen their useful life.
Your power supply is labelled 12V. This goes to the DPDT relay. Therefore its coil should be 12V. Its contacts need to be rated for maximum expected Ampere levels. 1A is reasonable since the diode type is rated 1A.
It's preferable if you can confirm it. Ordinary digital multimeters which I've owned can measure up to 10A.