Because you've bought an MTL atty it will probably get quite toasty at 30 Watts and above as they are compact, with limited airflow and designed to vaporise small quantities of juice that contains higher concentrations of nic. Direct to Lung tanks can run comfortably above 30 watts as they have much more airflow which mkeeps things cooler, but they vaporise much more juice, 'cloudchuck' and are best with lower concentrations of juice.
I believe the Berserker line come with a range of air inserts but I only have the original RDA so I'm not sure about later models or the RTA range.. When I used my Berserker regularly I found that if I used the air inserts with smaller holes, and tighter air restriction it worked best for me at 12 to 14 Watts using 20mg Nic Salt juices. If I used medium sized inserts less restriction I had to bump up the wattage to 15 to 18 Watts, but drop the nicotine strength to 10mg or it could make my head spin if I chain vaped. Using the largest insert it was too loose for me for MTL vaping but really good for Restricted Direct Lung vaping and worked well for me at around 25 Watts.
When it comes to coils, I've used several Vandy Vape MTL and Coilology MTL wires and found them to be good - but as others have mentioned simple round-wire works just as well so don't feel you have to go for the latest, most complex coils. I use them and I think they are a TEENY bit better, bit quite honestly the difference could easily be in my imagination as I've never had any problems with simple round-wire coils in MTL tanks.
As you're using a fully regulated mod you don't have to worry too much about what resistance coils to use as you can manually adjust the wattage/voltage output and they have built in safeties so they won't go nuclear if you fit a build that is too low or you have a hard short.
From personal preference I tend to use complex coils in the 0.7 to 1.2 ohm range (or simple Kanthal 28ga round-wire coils if I'm out of the fancy stuff) for lower powered MTL vaping. For restricted DL I tend to use slightly lower resistance coils like MTL staples or slightly thicker 26ga Kanthal Roundwire, but that is just because I feel a little more comfortable using slightly thicker wires at higher power settings - not that I've ever had a problem using either.
I recommend you just experiment with the different airflow and power settings at first and just buy a small spool of 26 to 28 round wire to start out with. Don't worry too much about what resistance coils you must use or feel you must study Ohms Law when using a regulated mod - with Mechanical Mods that knowledge is essential, not so much when using a regulated mod. Just use physically small 5 to 6 wrap roundwire coils in your atty to start out and you won't go far wrong.