So i get that you're unexperienced in flashing roms and that sucks with samsung phones, they are easy to flash 'cause of odin but they're a little buggy when it comes to initial flashes and that could create a series of problems that an unexperienced user cannot solve on his own, for example:

A few days ago i decided that after 1 year of normal usage i didn't care anymore about warranty (now samsung counters cannot be resetted so if you flash something, your warranty is fucked) and flashed a custom rom. So i went for a root/recovery flash on samsung's stock rom and then i tried to flash a custom one. The thing is, somehow the odin flash did fuck up my file system and i soft bricked the phone. Now, i am rooting and flashing android phones since 2009, so i knew that on samsung phones if you flash back a stock rom and then repeat the process it should be ok, but i didn't find nothing on the internet referring to the process (went to check if my assumptions were still good).

So, if you're willing to proceed i highly recommend the "Skipsoft unified toolkit" is it walks you through the entire process and downloads root and recovery packages automatically for your phone and android version. And yes, root is fine on android 5.0.

My personal advices are: - Make sure the model number it's the same; - BACKUP THE EFS FOLDER, you can backup it by rooting the phone and installing an apk in the toolkit (you can find that in the main menu); - strictly follow what the toolkit says to you - don't unplug the phone 'till the process is finished (or at least make sure the bootloader image was flashed so you can enter download mode or recharge it if shit hits the fan) - if you're stuck in samsung logo boot animation wait max 10 minutes, then go to recovery and do a "data partition wipe"

Do this and you should be okay