of course its recommended to start training to prepare yourself
before enlisting. this way you wont suffer as much while in there.
what you mentioned should be more or less enough. but you may wish
to vary your training, perhaps to increase the running distance or
speed, or vary your statics every now and then. the purpose is to
ensure your fitness level increases generally and
comprehensively.
the percentage of a cohort going to OCS is more or less constant.
the jan and apr cohorts, which are the JC cohorts, should have more
or less the same number of persons going to OCS as the other
cohorts. hence to say that a high percentage of JC students enter
OCS is not quite right but not wrong too.
for OCS you would have to indicate your preference for command
positions during your bmt. as for guards, you may state your
preference to your PC but in the end its up to the requirement and
your PC. and CDOs are different - they are enlisted directly to
CDO, go through CDO BMT, and CSLC. only those who have performed
remarkably would then join OCS midway through the course.