keeping in mind that the handguard is where the battery is kept, replacing this with certain RIS units basically takes the space away for the battery, so you'd need a peqbox accessory or rewire the gun to the rear and use a stock that can hold a battery.
There's not a whole lot of accessories to put on imo... a grip of some kind if that's your fancy, but almost everyone I see with a grip uses the magwell as a grip more than the foregrip or angled foregrip. maybe a flashlight if you are playing in the dark.. you wouldn't really leave it on when you're not using it.. just something else to get shot out. And like I said, if you go with a compact rail system, you will need to rewire or use a PEQ box to store your battery, that attaches to the rails as well.
the KA has a removable carry handle so there's a flat top rail underneath it to attach an optic of your choice. Most optics will fit in that amount of space.