Parallels 8 is an excellent product that is easy to use and integrates Windows 7 with OS X beautifully. You can also opt to simply fire up Windows in a Window if you prefer that for some reason. If you do, it is simple to full screen it anytime you like.
On your system for many titles performance should be fine with Parallels 8.
I do not think bootcamp is a good option for your system unless I am wrong about something which is, I think bootcamp requires you to install Windows on the startup disk which in your case is a small SSD. I would not be willing to give space to a Windows install on a 256 gig disk personally although if there is some game that simply won't run any other way, it's your computer, your life, etc.
When you create a virtual machine that Windows gets installed into with Parallels, you can have it live on the larger disk you have installed which for you would be nice. Parallels defaults to installing them in a Parallels folder in your Documents folder but I believe you can choose a different location for them in options. I just checked Parallels Preferences and yes, you can choose a location to store your virtual machines.
I find Parallels to be a truly impressive product that is elegantly designed. It should serve your purpose nicely but it would help to know what games specifically you wish to play with friends. There is a huge difference between playing Orcs Must Die and Battlefield 3 for example.
Keep in mind, DirectX 10 support in Parallels is brand new to the current version and a work in progress. Not many games require more than DirectX 9.0c currently, even if they also offer DirectX 10 or 11 features. In other words, most games will run on any GPU supporting DirectX 9.0c which Parallels does very well and with good performance generally. There are some new games that require DirectX 10 to run at all. I can't think of any off the top of my head but I am pretty sure there are some out there at this point. I would not expect them to run well in Parallels yet although hopefully next version they'll up the performance a lot there.
I don't tell you that stuff about DirectX 10 to scare you off but just to inform you in case the major game you want to play with friends is one of the few that requires it. Check the system requirements for the games you want to play on Steam carefully to ensure no unpleasant surprises.
For a lot of games, Parallels is a great solution that avoids the dreaded reboots of bootcamp. That is why I use it. People will often dismiss it in favor of bootcamp but I think it is a very useful solution too depending on what you want to play. If you are looking to play multiplayer shooters with friends, I would expect the Valve games to all work great for you with Parallels given your hardware. Brand new shooters your mileage may vary on a case by case basis depending on how hardware intensive they are. Even then, scaling back graphics options starting with resolution and then moving on to various effects would probably result in decent frame rates which are really important in FPS online play. You need that to run very smoothly to enjoy it.
In any case, your options remain open once you have Parallels and a Windows license. It isn't like you cannot do bootcamp later if you need it for a particular game.
I forgot to mention one last thing, I did recently read a review comparing the current versions of VMware and Parallels and performance-wise, Parallels came out ahead in every measure. It also came out ahead in terms of features.
