staph/strep

[ying]

i want to isolate staph and strep.
                          Sample
                                |
                       Gram stain
                                |
          Colombia nutrient agar
                                |
                         Catalase
                      |                     |
                    +                   ( -)
Mannitol salt agar
                    |                       |
                    Heat tolerance
                   Biochemical test
Question
1.    Will this method worked?
2.    If catalase test is (-), can I confirm the sample contain strep?
3.    Are there any possible contamination from other gram positive cocci?
4.    Any other suggestion or comments?
5.    Is it necessary to plate the sample on mannitol salt agar (if catalase
test is positive) to select staph?
6.    Can I substitute Colombia with any seletive media for both staph and
strep?