Ok well it's plenty strong enough but I would use 2 x ballscrews on the Gantry with this wide Y axis design to stop any racking affect but connect with timing belts using one motor.
I would use 20mm diameter and 20mm pitch screws at this length with a ratio applied. This will give more torque allow lower screw speed and still maintain decent rapid speeds.
Regards the motors then be aware that large nema 34 motors spin slower and require high power drives. So for this reason I'd go with 6Nm or no more than 8Nm motors as they will spinn slightly faster but still will require high power drives to get the best from them.

20mm linear rails will be more than enough.

With this wide gantry design you make it more stable/stiff but your making life hard regards the Z axis and you'll need to work on this area because that simple frame won't be enough. To be honest I'm not a Fan of this style of gantry design because it makes life harder than really needs to be and for not much more gain really. If your just cutting wood then you need to ask your self do you really need this complexity and my answer would be No.
Also to take advantage of the extra stiffness the gantry allows you need to have a powerful spindle so again not much point if your just using a plane old router or 2.2Kw spindle as a conventional gantry design built strong will be more than good enough.!!