Hello Guys, I have few questions 
:
Does it play a crucial role to hand off design: how I create icons and logos (in Sketch): group elements or create symbols?
If I am going to download icons and other elements from free resources for company’s project, is it allowed to use them for business needs, or I should request a permission?
If someone can share resources with free icons, which I can use not only for my portfolio, I would be extremely grateful? 
…Anyway, Thanks in advance!
I don’t use free resources anymore. I’ve found that the quality or resources a lacking. While it’s not the best out there, I use freepik.com. However, there are free resources out there, I’d just google free icons for commercial use. Not the greatest answer but talk to your company about using 2nd level resources. They aren’t as expensive as adobe stock but responsible and provide good and vast amount of images.
Each distributor and each owner of every copyright has its own rules regarding how their materials are used. There is no one-size-fits-all answer to your question. You’ll need to look through the End User License Agreements on each of those sites to find out what their rules are.
I don’t use the icons created by anyone else unless I paid for them. In Europe, it is pretty risky to do so, as the copyright is applied there and all rights belong to the designer (company where this designer is working on). Last time, I purchased the package of icons (“majestic icons”), even though these guys have about 400 icons as a free pack. Maybe these 400 icons will be enough for you.