Read a contract. You enlist in the Naval Reserve in an inactive status.
The rest of the stuff you've mentioned is all admin stuff spelled out in various laws, regulations and instructions.
BTW, while you do not accure any time in service, I believe your PEBD (pay entry base date) is the day you sign your OCS contract / enlist in the reserves (it was in my day) which means you get the pay bumps quicker.
Very well, however, OCS accessions are usually at OCS within a couple of months at the MOST as opposed to BDCP guys, so the PEBD as opposed to TIS is a minimal difference.
BDCP time in service = day sworn in. For me, I was "active duty" ~1.5 years before I commissioned = SWEET! I was an ENS (however, >3) when everyone else was a JG, and as soon as I made JG >3, I was suddenly making more $ than everyone else who was still JG > 2. GOOD deal!