fall rush or spring for sororities

absolutely re-rush in the fall! every sorority will 100% take sophomores. I can't speak for every house, but I do know that some houses even have a required number of sophomores to take! your chances as a sophomore are just as good (if not even better due to having friends in sororities) as your chances as a freshman.
Spring rush, however, is a lot more selective and basically is for girls that are already friends with girls in the chapter. (again, not all the houses are like this but many are.) spring classes are limited and usually only a few houses even take classes. on top of that, it'll most likely be a small and very selective group, most likely 10 girls or under. because of this, i highly highly recommend trying out fall rush. its a great experience and you should go for it!

Yes

It will help if you were polite and up-front with the women whose home you had to drop, and also if you make sure you are up-to-date with them financially. Leaving on good terms makes life easier.

Please take the advice given above and recruit this Fall. But also understand that some homes have the private national recruitment policy of being unable to invite you beyond open house this year because they cut you from their lists last year. It's called once dropped, always dropped. You will never know which houses have the policy and DO NOT ASK! It may sting a bit, but the best way to think of it is: fewer houses to worry about, and it only takes one bid to belong.

You should have a brief but polite sentence or two to explain your decision for dropping last year incase your recruiters inquire about same. Nothing bitter, only simple, as you are now moving forward.