if my phone gets stolen, and i erase my iphone in lost mode, will all info/pictures and everything get deleted? just like it would do when reseted?

Yes, a remote erase will completely wipe it of all information. You can also enable the erase data mode for your screen lock passcode so it self erases after 8 (or maybe it’s 10) failed passcode attempts.

See the manual - https://help.apple.com/iphone/11/#/iph14a867ae

If you have a passcode on the device they wouldn't be able to access anything on your phone but the following excerpt has information about erasing using Find My iPhone: (from) If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Erase your device. To prevent anyone else from accessing the data on your missing device, you can erase it remotely. When you erase your device, all of your information (including credit, debit, or prepaid cards for Apple Pay) is deleted from the device, and you won't be able to find it using Find My iPhone. After you erase a device, you can't track it. If you remove the device from your account after you erase it, Activation Lock will be turned off. This allows another person to turn on and use your device.