I'd like to get a consultation about the work permit and a simultaneous side job in Switzerland. I am now based in Russia and my Swiss employer is working on the permit for me (B permit or L permit, I think - now I am just a contractor). I am also having other clients around the globe which I wanted to serve from Switzlerland as a side job (self-employment or sarl). Is this possible with B or L permit? Please advise.
You would need an unrestricted B permit. For non-EU, B permits are usually restricted to a single employer. Even if your other clients are outside Switzerland you cannot work for them from Switzerland.
Tell you prospective Swiss employer and they may be able to arrange something. But you cannot do anything yourself.
As said usually non-EU national permits are tied to the employer and you can’t be self-employed or start a business here.