haha, my 10 is split 3 ways! Don't worry splitting once still gives them 5 gallons to swim in! They'll both love it ^_^
As for filter, nope you can just use on filter! mine is baffled with a soda bottle piece so it actually flows out the sides so it circulates through the dividers. And then the heater is right on the side of it so it circulates the heat throughout the tank as well.
For dividers, there's actually DIY dividers you can do yourself: http://www.tropicalfishkeeping.com/d...ividers-21866/
which are pretty nifty. I just use the plastic mesh and make it a tight fight and I haven't had any problems with it! On my Lee's divider I bought from Ebay I had to double the mesh so that they couldn't see each other well so you can do that and it will make it easier on them. They will flare for the first two weeks or so but don't worry, they'll get over it soon and then won't care about each other
Here's a link to my filter baffle if you want to see how that sort of works: http://s1292.photobucket.com/user/li...ilter%20Baffle
And here's what the actual tank looks like. I do have a small internal filter on the leftmost side facing in but if it's only divided once, it's not necessary.
You can see I have Lee's divider which is the blue one and then just the plastic mesh with no silicone or anything holding it in besides force
it's been like that a good 3 months now with no problems.