Star Marine as a separate entity is canceled. The content has instead been wrapped into the main game. I'm also not sure if we are going to get alpha 2.6 or if they are just going to plunge into alpha 3.0 towards the end of the year.
Ok now to the other bit about ordering.
I really would not suggest just picking up Squadron 42. You are not getting Star Citizen if you do that, you will have no access to Star Citizen proper, only 42 which is a single player campaign kind of like the old Wing Commander games.
If you go here
https://robertsspaceindustries.com/fly-now you can pick a ship, I would suggest picking the Mustang Alpha. They both cost 45$ but the Alpha is worth 5 dollars more than the Aurora MR. You can also add on Squadron 42 for an extra 15$. After you do that, I would strongly suggest upgrading to an Aurora LN for 5$ more bringing the total to 65$ USD. or about 20$ more than just the Squadron 42 package.
The Aurora LN is a very good ship. It's a capable fighter, and you can outfit it later to carry a large cargo pod which would be useful for trade. Best of all it has a bed (which is important to saving without going to a station).
Aurora LN
https://robertsspaceindustries.com/p...rora/Aurora-LN
Also if you happen to want to upgrade further or buy a second ship you can do that, either from the standalone ships list
https://robertsspaceindustries.com/p...?product_id=72 or the ship upgrades page
https://robertsspaceindustries.com/pledge/ship-upgrades