Amp and head pairing

I know that most of you view this as common knowledge but I have only ever owned combo amps..so this is my question; what do you have to make sure of, if anything, ohm wise and what not to pair a cab with a head?
Enjoying some of their tube effects in the past, I recently played the Blackstar Ht-5 combo and it is an incredible amp if you consider its price and its features. It's great for me, but I want to run the head through a 1X12 for a fuller low end instead of the 10 inch speaker that comes in their cab. (or combo) Being that it's 150 bucks cheaper to get the head alone, it seems like a no brainer for me to get what I want from the get go so thanks for the knowledge on electronics, I wouldn't wanna ruin my brand new gear.

When you connect a speaker cabinet to an amp you need to make sure that the impedance of the cabinet (the ohms) mathces up with the expected load of the amp. The HT-5 head allows you to connect a speaker cabinet with an impedance of 16ohms OR 8 ohms. That 8ohms can be made up of one 8ohm cabinet OR two 16ohm cabinets (which means that the speaker outs are in parallel). You cannot use all three outputs.

As long as the 112 cabinet you get is connected to the right speaker out, you can use whatever you want - you can run 2 412s if the impedances match - and it wont ruin the amp.

If you need any other help I'd be glad

Thanks alot man. I pretty much knew that the answer I would get would be that but I'm a reassurance kinda person so much appreciated. I doubt I will ever need a 412 considering I can be easily heard with a drummer with a 112. Plus I'd probably get a bigger head to push it if I did but again thanks for the reply. I posted the question on the g&l board instead of an amp forum or something cuz you guys are always super knowledgeable and not judgemental. I gotta start somewhere..

A 2:1 mismatch is acceptable. Meaning with a 8 ohm output you can use a speaker with a impedance from 4 to 16.

Craig