I wonder how I can change a weapons' reloading time (not retrigger time) through the config files? Or it's hard-coded in the animations? (I not found any threads, where this question is discussed)

It is animation controlled, i.e. reload animation duration decides the reloading time.

An animation can be easily duplicated in soldier_animations.xml and have its playback speed changed. A weapon's reload animation can then be pointed to the new animation.

Oh. Thank you.

What is the best weapons to choose with in this kind of game, as I have no idea since this is n\my very first time of using the site?

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shuriken stars

There are no "best weapons". It all depends on your game style. If you want to spread bullets, if you want to be sneaky, if you want to have high fire rate, low reload time, etc.
I think the standard assault rifles (G36, M16, AK47) are the best choice overall.