New To Strat

Also can I play online with the cdrom version with other managers?
Can you play in an online league as well?
If you can connect then how do you connect your sessions?

As for rosters I don't need to buy the game again but just the roster.

Absolutely!

PCGame players basically compete in 3 kinds of leagues, almost always some kind of keeper league:
1. Head to Head using "netplay"
2. Home (or Away) vs CM
3. Play By Email

Head to Head Netplay:
You need the PC game and the season roster for the league you are playing in. You play all of your games head to head over the intenet against your opponent. The season is split up into blocks (either a month or a week) and you have a period of time to coordinate your games with your opponent and play them. Netplay games can take anywhere from 30-45 minutes to play each game. Once the games are completed, the hosting team sends the game files to the league commish. Connecting requires port changes in your firewall. There is a large group that never have a problem with netplay, there is also a smaller group that have given up on it due to connection problems. The community has figured out its own work around using a screen sharing app called "Team Viewer".

Home (or Away) vs CM:
You need the PC game and the season roster for the league you are playing in. You submit your CM before each block of games, then you play all of your Home (or away games depending on the league structure) games against your opponents CM, and then send the game results to the Commish. A fun way to play, doesn't require scheduling big windows of time with your opponent. Down side is that you will occasionally run into a manager that replays his games until he gets wins. Experienced commissioners have checks and controls in place to limit it. Also, leagues that have been established for many years typically have the unscrupulous managers weeded out.

Play By Email - typical
You need the PC game and the season roster for the league you are playing in. The is very much like the online game, you set your CM, send it to the Commish and he runs each block of games, CM vs CM. My favorite by a wide margin.
I run leagues like this, modified, so that all you need is a computer with internet access to play, no need to buy the season roster or the game.

There a wide variety of leagues - keepers, salary based, usage limits, spanning all eras.

Here's a link to my leagues site, currently playing our third decade of keeper leagues, we started in 1950 and are now in 1970:
http://www.stratomaticnation.com/sombb/1970kp/1970/standings1.html

Some other examples of leagues (I host the stats pages for them), just a very small sampling of the leagues that are active:
http://www.stratomaticnation.com/sombb/statpack.html

Here's a link to Strat-Fan-Forum with tons PC game based leagues that are always looking for openings:
http://www.stratfanforum.com/

Strat-fan-forum also has lot's of great resources like better ballpark images, player image packs, etc.

Welcome to the world of Strat!!!

Its addicting.