Shorten the cocking rope to a minimal length and it will make the cocking process easier, especially if you are 5' 9" or shorter.
Your bow is made by PoeLang for CenterPoint and like the company that makes the Sniper, the triggers are poor. They have a long pull (1/2" to 5/8") and a relatively heavy break pressure (6-8lbs). The M390 is just like the Tormentor so addressing the trigger issue is the same. Shoot it a bit and if you can't stand it, do a search here for Tormentor Trigger and read through that thread.
If your Mercenary is the "Whisper" package you already limb silencers and the butt stock has an adjustable cheek pad. If it's not you may consider those two additions.
Take care of you strings and keep the flight rail lubricated but not over-lubricated. Look at the products from Scorpion Venom to do that.
The 20" carbon arrow are OK but don't be surprised if there is a flyer, possibly two. Add getting better hunting arrows to your "to-do" list.
Use a proven Xbow rated broadhead, preferably one that flies like a field point. I use mechanicals and have had excellent performance from them. Specifically the 3 blade, 1 and 1/2" cut, Grim Reaper Razortip in the 100 gn weight. Their packages will be marked "Xbow Approved".