Hi all. Can I use pins 3v3, vin and 5v if my modules will be connected to them in my circuit? (attached the picture). Or should I avoid 3v3 and use only 5v to connect the modules and vin for the battery? I'm afraid my arduino nano won't be able to handle the voltage or something. Sorry if this question made you laugh, but I want to know the answer. Thanks in advance.
Your Arduino is not a power supply.
Multiple low power devices can be connected to 5v and 3.3v.
You must keep current draw to a minimum.
If in doubt, get a buck converter to generate the 5v and 3.3v for external devices.
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Thanks for the answer, mate. So there's nothing wrong with my circuit?
Looks okay as long as the voltage regulators on the Arduino run cool.
Always observe proper polarity with your power connections. 
If that’s a laser diode, it may not last too long powered on all the time.
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Thank you, thank you, and thank you again. One more question if you don't mind. And if I connect that oled 128x64 not to 3v3 but to 5v like all the other modules, should everything be fine too? It's just that for some reason everyone connects it in 3v3
All devices required a voltage of a specific value.
Some displays need 5v some need 3.3v
You must follow the data sheet for your particular display.
If you power a 3.3v display with 5v, you will damage components.
BTW, a 3.3v powered device may need the logic signals sent through logic level converters.
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Thank you again, Larry. 
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