First off, I'd like to apologize if this thread has already been posted elsewhere, but I'm still new to the forums, and still new to the whole 'Firebird Community', as it were. I purchased a '98 Firebird Trans Am (WS6) with an automatic transmission about a month ago, knowing a few codes had been thrown by the computer because the previous owner had removed the cats. I was perfectly alright with dealing with that, because I've got a scanner, and I run diagnostics every couple of weeks just to make sure. That's where the story begins- it's thrown a couple more codes, and I was wondering if you lot could help me identify and get them sorted out. The exhaust on the car has been swapped out, and they've installed a hypertech hand-held tune on the vehicle. Other than that, the vehicle's entirely stock. Let's get into it, then, shall we?

Code: P0102 - OBD-II Code P0102 is defined as a Mass or Volume Air Flow Circuit Low Input
Code: P0103 - OBD-II Code P0103 is defined as a Mass or Volume Air Flow Circuit High Input
Code: P0138 - O2 Sensor Circuit High Voltage (Bank 1, Sensor 2) - CATS
Code: P0158 - Oxygen Sensor Circuit High Voltage (Bank 2 Sensor 2) - CATS
Code: P0410 - Secondary Air Injection System Malfunction - CATS
Code: P0412 - Secondary Air Injection System Switching Valve A Circuit Malfunction - CATS
Code: P0418 - A P0418 trouble code is an indicator that a problem has occurred in the secondary air injection system. - (In direct correlation with P0410 and P0412) - CATS
Code: P1258 - Coolant Related, injectors disabled.
Code: P1415 - Secondary Air Injection (?) - Possibly CATS

With regards to each of the codes:
Any code with a description followed up by 'CATS' is something I've marked and personally assumed to be associated with the catalytic converters being deleted. Please do let me know if I'm wrong with those, and if it's something I need to worry about. I'm not looking to put the cats back on, but I am wanting to keep this car running at its possible best, because I have formed quite the bond with the thing. As far as the (P1258) Coolant code goes, I simply assumed it to be my coolant level sensor, so I took a day and replaced said sensor, and I've replaced the coolant in the car. I've checked time and time again, and nearly pulled my hair out trying to find any sort of leak in the coolant system. Should I, instead, go for a full coolant system flush and see if that nets me any results? As for the MAF codes, should I get an MAF cleaner and try to clean it before doing anything with it? I checked the wires, and they seemed to be alright, and the connection seemed secure.

TL;DR - Having trouble with codes, I've tried diagnosing them to the most simple degree, no luck. If you could leave suggestions as to how to solve my problems, that'd be great. As always, I appreciate the time and efforts of the folks who'd help me with this. For the curious- I'll post a few pics of her.