The whole thing about smoking meat is you learn as you go! Don't get discouraged as without failure, there is no getting better.
To help with the temp swings.. go get yourself a welder's blanket and magnets to hold it onto the cook chamber
here's the one I use:
https://www.harborfreight.com/6-ft-x-8-ft-fiberglass-welding-blanket-95015.html
magnets:
https://www.harborfreight.com/2-piece-craft-magnet-blocks-98406.html
the Austin has a 3ft cook chamber so this blanket can be folded over to add more layers... the magnets I have 3 sets and they hold the blanket even folded over some much easily. I got 4 magnets on the lid and two on the back of the chamber and even a windy day won't move it physically. I've even used this on very very cold days like 14 15 degrees and p2 p1 with the blanket its been steady
right now I got a brisket on and with the P-setting of 4 and blanket its hanging steadily from 175 to 200 which I'm fine with as I'm only using it for smoke flavor for a couple hours then turning it up.. I could have gone with P3 and it would go up to 185-190ish to 230 but some swing is fine
I've done some things with rubs that made me palm -> forehead afterwards for using it... Mango Rub sounds like it should be on fish or fish to me... and don't underestimate using simple rubs like SP, SPG or SPGO... meat should have good natural flavors
** if you want me to post a picture of how my blanket in on my smoker for reference let me know