[Galaxy S II Q&A, Help & Troubleshooting] PantsDownJedi:
Everything is pretty scattered even for people who are sort of on the lookout and have tried various newer ROMs.

Dualboot is a feature in custom kernels, at least Siyah that I know of, where you can have more than one ROM installed and choose at boot time which one to use. I gather that its mostly useful for people wanting to try the experimental builds of Jelly Bean and have a stable Ice Cream Sandwhich.

Aroma is an installer which is sort of a second step after a CWM flash, and before an install, and allows you to choose via checkboxes which extra options you might want. This is up to the ROM maker as for what selections you might have. Examples are sometimes which kernel, which Samsung apps that aren't included in the ROM, etc.

I don't know what mali and vsync are but I would guess that vsync has something to do with graphics and maybe with the experimental Jelly Bean builds.

The only really important thing I can thing of is, as always, to do a nandroid backup before starting anything and possibly since you have Gingerbread you might need an older Kernel on hand with older CWM for a recovery back to Gingerbread... This needs to be addressed by someone who can clarify and it might also be necisarry to flash a newer kernel and CWM that will allow you to enter a recovery mode that will be compatible with newer ROMs but I don't know if this is the case or not. Again, this needs to be addressed by someone more helpful.

More important than the above is that, since you've apparently been out of the loop for a while, there's been a bug that can render a hard brick on some devices depending on various hardware components and the version of CWM used for flashing. There's a sticky thread about this but the safest thing way to go about it, as I understand, is to just not flash a 4.04 ROM but use a 4.03 one. I've used both and prefered the options available in 4.03, for my needs, as far as mods go.

Also, as for Jkay's work, some ROMs incorporate that and some incorporate similar features but aren't near as feature rich. As with Gingerbread there's only so many ROMs that he's done the work for and it now requires not just flashing of a framework, as was in Gingerbread, but purchase of the app from Google Play that will allow you to customize the settings. The thread is here http://xdaforums.com/showthread.php?t=1667846

As for theming, its easier to choose a ROM that has it done already and is compatable with Jkay's framwork (assuming you want those things). You can, use a stock ROM, theme it, install Jkay's framework and it will work quite well but its more work. Vertimus themes are very popular but the site navigation is confusing and will definately be daunting. It would be necissary to read first before making any changes (themes or tweaks) deviating from initial setup. The easiest thing is just to choose something, assuming you want it, already themed and tweaked for Jkay's app to work in advance. Wanam builds seem pretty popular for this and as for the hard brick bug possibility with CWM on 4.04 ROMs, you can probably follow the current Wanam build download into his site and find his forum, search for a 4.0.3 ROM (LPG has played best with my particular handset) and make sure its for the SGSII as people often build for more than one phone and it would be a shame to flash an SGSIII ROM (or something else) on accident, for example.

My recommendation, in summary, is not to worry about dual booting or those other things for the moment, do nandroid backup if you intend to upgrade, find out if you need to have older CWM to downgrade (a flashable one at that in case you get stuck at a boot loop) or a newer one to upgrade, then keep it simple and choose an already themed and Jkay tweaked (you'lle have to buy the app) ROM that isn't a 4.0.4 build of Android, but 4.0.3, and to stay with Samsung based ROMs as a starting point. From there you can get a feel for for things and decide if you like the theming or if you want flash something else with stock Touchwiz, if dual booting is worth the trouble, and then bother to read about the other things you mentioned that I wasn't able to answer... so basically, keep the upgrade simple and then go from there and quite frankly if that means a stock upgrade to unmodified Samsung firmware then so be it.