hello,

plaxis is a FEM software which means that it considers the continuum mechanics principles. simply put, it means that materials are fully, moderately, weakly bonded without any discontinuity like cracks. 

although you may model faults with plaxis but in general, you cannot model a weathered rock with discontinuity otherwise you have a intact rock.

I suggest you to work with UDEC if discontinuity matters for you

regards,

Yes, you should use Jointed Rock Model or change your parameters according to the other models.

I suggest that you use UDEC software which is better than for this case.

Best,

Absolutely, you can use the program to model soil and rock slopes and find the factor of safety

You can use PLAXIS for estimating the stability of rock slopes using strength reduction technique. Read the following paper for more details and solved example in PLAXIS.

If your medium is dense rock or very broken rock, the answer is yes, But if in your medium is less than 4 joint set, you should use other softwares like UDEC.