Fighters can attack as long as theyre within 2" range, the issue about numbers contacting the stem only really comes into it with suicide fighters (gaim and dilgar) or targets with stealth. And yes you can shoot at fighters in base contact with enemy SHIPS but not if theyre in contact with enemy fighters (theyre in a dogfight).
As for your fleet selection:
Nova - Personally I think the nova is a fantastic ship, its heavily armed, tough and carries a sizeable fighter compliment, however for facing a fast maneuverable opponent like the ISA It's just not worth it as they will just avoid it's guns until they have taken out it's escorts and can then move gank it at their leuisure.
Hyperion - The hyperion Heavy cruiser is an ok ship, but personally the Raid level hyperions are too fragile and die too fast. The SKIRMISH varients though, in particular the rail cruiser, are truly phenomenal ships. They are not as well armed but are hard as nails for their PL.
Avengers - As noted, when fighting ISA, fighter swarms are your friend. An avenger filled with fighters is a nightmare for most ISA forces. However if he's deploying that Dag Kar, stay back and keep em in the hangars or out of range till you can blast that thing off the table with long range missile fire.
Saggitarius. Nasty on it's own, in numbers it's verging on broken. Still the same can be said about the whitestar so imho go right ahead and fight fire with napalm
Tethys. As it stands wonderful initiative sinks, but that will soon change. Still handy for 'maneuver to shield them' though once that returns.
Hermes - Alos highly underated, and wonderful for taking on the ISA, fast (by EA standards), maneuverable, long ranged and even carries a fighter flight. This ship practically SCREAMS 'take me' for fighting ISA.
As for fighters, ordinarily I'd champion the humble Tiger star fury for it's missle range but seeing as the ISA fleet will still likely have a few nasty things like Nials and maybe even an carrier Auroras are probably safer. Also Auroras actually stand a chance of catching up to Whitestars
It's also worth noting you dont have to just get in his rear arc, use the sides too

He's only got forward guns on most ships so swarm with as many as possible and as noted with self repairing adaptive aromoured, dodging little monsters:
"There is no 'overkill', there is only 'open fire' and 'I need to reload'"
Pick a target and shoot it till it goes boom. Never EVER leave a whitestar/bluestar/whatever crippled/damaged but still on the table.
My 5pt raid fleet would be:
2 x Saggitarius (1pt)
2 x Rail Hyperions (1pt) (carrying Auroras)
1 x Avenger (1pt) (loaded with Auroras)
4 x Hermes (1pt) (again Auroras)
1 x Oracle and another Saggitarius (1pt)
Turn 1: All missiles make DagKar go away. Use scout lock and avoid CAFing with fighter carrying ships etc. End of turn launch all fighters.
Turn 2 onwards: swarm ISA with fighters, keep fleet together so they cant pick you off one at a time and hammer one ship after another. Start with the blue stars, they die quicker and are almost as dangerous in my eyes but if you get the chance to hit a whitestar hard, do so but make sure you finish it.