So, the pistols do count as a second close combat weapon? And the soldier carrying them gets to attack twice, even if they have A=1?
Well, I do intend her to have the Blade of Admonition, as well as two other relics that grant bigger protection... Also, I plan to support her with a Command Squad, but that's in the future.
Rhinos / Immolators are expensive... As for the special weapons, I bought one Sister with each for the collection's sake. I plan for each squad to have one special weapon and one heavy weapon. So, one squad will have heavy bolter and a flamer, the second one will have heavy flamer and a melta etc.
Hm. My plan was to keep in the second line and use them if the army runs into something they won't be able to gun down from distance...
Exorcists are mightily expensive! I plan to get one... in the future.
Remember I want to have an Dark Eldar army and a Chaos army, too... And I don't earn that much...
Pistols add +1 to your attack. So if your model would normally have 1 Attack, equipping it with a pistol gives it a second attack. Bear in mind that some of the models with have this already added to their profile, but normally it will be noted that it has already been added.
You'll probably need to give your canoness a jetpack or something to make her effective. Footslogging your sisters across a field, especially if there's little cover, is going to be difficult. That goes for the Repentia as well - most people who know what Repentia do will do anything they can to take them out before they can get close. They're a fire magnet that doesn't have that much self-protection. Also, Sisters aren't really a ranged army at all - they're most successful between 1" to 12". Shooty armies will outshoot you if you try to shoot them, and sisters don't have the firepower at >12" to keep assault armies at bay.
I know vehicles are expensive =P I've spent money on them myself. But sisters are already very difficult to play - they're not incredibly tough, and you have to get close, but not in melee range, it's pretty difficult to pull off. That 3+ armour save isn't as impressive as it sounds - when you lose half your sister squad instantly to a single shot from a Leman Russ you'll understand how painful it is. Back in 4th Edition you could turn that 3+ armour to an invul save; but now you can't, so you have to be a lot more careful with them. Now, more than ever, you need extra protection, and larger squads as ablative armour for them.
Especially Repentia - those girls are really, really flimsy. They will get murdered horrible if you put them on foot. On the off chance that you manage to get them into melee they will rip everything apart, including most terminator variants, but problem is getting them there in the first place. Also you need to run like fifteen in a squad, not just 6.
If anything, field larger sister squads and get Exorcists. Exorcists are the mainstay of a Sister army - they deal with so many good things at range. In fact, if you're playing anything higher than 1000 points, I'd recommend getting 3.