Using different types of batteries (with different chemistry) is definitely NOT. Another option is to mix lithium and alkaline batteries. If you want to use the paired set in mods with a single battery, you can, BUT you should NOT use it as a paired set again. Mixing lithium and alkaline batteries is another resounding NO.
Use a regulated mod and it's not a problem, but you have to consider its operating voltage. In some cases, if you use 8.4 V, your vaping mod will turn off if its “cutoff” limit is lower than 8.4 V. In other cases, it could damage the vaping mod, as a maximum supply voltage of about 4 to 5 volts is expected. Now I'm back, and since I'd like to quit smoking without murdering anyone, I thought I'd go back to vaping.
I used to use a 20 W blade, but I'd like to start vaping in MTL, probably along with the Blacknote liquids I've seen. As for the style, I have to say that the Proton Kit looks impressive, but I think it's a bit over the top for my plans and, you know, I'd like to go on MTL. When it comes to a suitable device, the options are endless and it depends only on your preferences. There are a lot of dual and triple mods available right now.
Whatever you choose, just make sure that the 30A limit of your batteries is not exceeded with the coil you are using. Unless you're totally new to the world of vaping, you're probably familiar with dual-battery vaping devices and 18650 vaping batteries. The Funky Lands Ti7000 also features Quaq Tech mesh coils, offering a superior vaping experience with a smooth and tasty vapor.