RADIOSS BLOCK - NON LINEAR ANALISYS PROBLEMS

Hello together,
I have a question about a non linear analisys using RADIOSS explicit (Block110).

I'm studing a composite component, using a MATX25 card for the material. The component that I'm studying will have large deformation , and for these reason I'm using a non linear analisys type. It's a flexural analysis on a plate like a leaf spring.
I have some question about mesh type and dimension (using shell elements) :

1)How I can choose element dimension? There's a formula or specific rule? I ask this becouse I know that it depend by timestep, or better, the two issues are related..

2)I tried to use a SECOND ORDER element type, but the solver doesn't work; I use a first order element type...is a compatibility problem from the MATX25 or how I can use the second order elements?

While about the material formulation :

3)For these kind of analysis I used, in a MATX25 card the CRASURV formulation. I seen that there was a Plastic Strain from low values of load and when the load go to zero, the component don't return in the original position ; I think so that this kind of formulation is not the better for the problem studied. Can you suggest me something about it?

I've done some laboratory test and the model has a less stiffness compared to the realty ( three times..)

Thanks
Best Regards