Hey man
Overall, some pretty poor advice on here. Let me help you out.
I am an active duty Marine Pilot and former collegiate athlete. The process for joining is not quite what he been described above.
In the USMCR going the officer route is pretty tough. Reason being the training for a given job is about 6 months longer than other branches. While I'm not 100% sure on the initial process it goes something like this:
Contact a local OSO
They specialize in officer recruiting and will help you put together your application for the next board the will meet and select the top candidates. You will apply as a "ground contract."
If selected at the board, you will then be given a report date to OCS (while not advertised, you don't have to accept if you are selected). Attrition rate hovers around 40% for OCS- it's not easy. But as a runner you won't have issues as long as you aren't a weak b!tch.
If you pass OCS you will commission as a 2ndLt and then head to "The Basic School" or TBS. This is a 6 month infantry school that teaches the basics of officership and leading a rifle platoon. At the completion of TBS all officers, with the exception of Law and Air (neither are an option for you as a reservist and with no law degree) will be assigned their official military job. This is the weird part for reservists.... You will probably have a good idea of what this will be prior to applying as there is a finite number of reserve USMC officer positions at your closest Reserve station (where you will be working).
Once you are assigned your job, you will then head to a formal course to learn your craft. This can be anywhere from 8 weeks to 6 months.
Once complete, you will head home and begin the "normal reserve schedule."
In all, the process will be around 1-1.5 years till you get back home.
The reserve route is tough because of the length of training. But good on you for considering it. Let me know if you have any other questions. Happy to help.