Is it possible to have a macro that lets me do soulburn and then soul swap, rather than using my sb hotkey, then the ss hotkey?
/cast Soul Swap
This does precisely what you're looking for. Watch out, though, there's no protection of you can't cast soul swap on the target. If you hit the macro while not targeting something that can be attacked, it'll burn a shard and just leave you with the Soulburn buff. Make sure you have Soul Swap without the macro somewhere handy just in case this happens.
Also, and this is a bit embarassing, wth is a mouseover macro? how does it work, that is, how is mouse over targeting different than tab or clicking the target?
Mouseover macros cast on whatever target your mouse is currently hovering over (this can be the actual avatar of the player or NPC in the game world, or a unit frame for them on your UI, like party frames). It does this without you having to target them, so it saves you the time waste of targeting them, casting your spell, then finding and retargeting your previous target. It's good for quick reaction stuff (like Mortal Coil), or stuff you want to cast on secondary target without actually changing your targeting focus (like Havoc).