Hey, I'm starting up a sisters army too (slowly).
I don't really have much in the way of experience with it or suggestions, but my impression is that the icon bearers are quite useful now in the new e-book, so you might want to pick up a few of those for your squads. Other than that, your list is basically what I have except with a few more sisters and a few less repressors (forge world rhino-like transport).
If you wanted a flyer, and the people around you are ok with forgeworld, there was one forgeworld flyer that the sisters can take as a heavy choice. I looked into it briefly, and it doesn't seem awful. Of course, allying IG is a perfectly legit option as well if you prefer the idea of inducted guard etc. And the valkyrie remains a bargain.
Other than allies, I'd look into more transports for your sisters I think. Immolators, rhinos, and/or repressors if you can do forgeworld. I'm not really convinced that they can function all that well if they have to trudge across the board on foot (although, again, I have way too little experience to make an informed argument there... just armchair generaling). Maybe find yourself a counter-assault squad of some sort, either via allies or by trying to play with some of the combat options in the sisters book, such as they are.
To be honest, I don't really expect GW to update the "archaic" sisters range anytime soon. Especially given that they've already had their book released, and it was done as an online only sort of supplement. I don't really mind though, as I actually like the metal minis (pricing aside). And while they're old, I think they're a fairly solid range on the whole. Anyways - if I were you, I wouldn't hold my breath for updates in plastic in the near future (but who knows).