Hi Point or any aftermarket mfgr. doesn't make 30 round mags for the carbine. I think many people wish they did but if you were to empty 30 rnds. through a Hi Point Carbine the Composite material around the stock would start melting from the heat. Haven't shot their pistols, held all, some statements say, it feels like a cordless drill, big and bulky pretty much correct.
The most logical out of the group mentioned would probably be the 9mm Glock models, which is on my list as my next purchase. I'd still purchase 4 extra 31/33 rnd. mags though. It just puts the weapon up to a whole different level but if you can't solve your situation in 15 rnds, your already a goner.
There is an after market adapter that turns the Glock in to a shoulder fired tactical weapon(read a little about this but can't remember the mfgrs. name). You just basically insert the pistol, no mods to the pistol. Hasn't got much media coverage so that might say, either it's too expensive for what it does or it a POS.
Lastly if you don't have a 12ga. shotgun and your needs are for home defense. Get a shotgun first the various loads cover every thing from hunting to H.D. Good Luck!
JT