Welcome to the forum.
In my opinion the single best "upgrade" for all guns is plenty of ammo. Shoot the snot out of it and then you can consider accessories that make it easier and/or more comfortable for the shooter.
I mean, the sky is the limit. My upgrades always have to make sense and have a benefit, I don't care too much for looks.
Might not be the answer you were looking for but I recommend you to hang on to your money and rather buy ammo. Shoot it plenty and then go from there.
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Jorge
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