Go to Settings on your device, choose Accounts and find Google Account. If you still have not added one, now is the good time to do that.
Then click on your account and tick the option "Contacts". It should now be synchronized with the Google server. You should repeat the same actions on the other device - that way the old phone will send your contacts and the new one will receive them.
Yes, Redmi 4A supports OTG function. If you are trying to connect pen drive please ensure that the file system is FAT 32. But it has a file size limit of 4GB only. You can check the complete specifications here.
You can also check this Video for detailed information:
You can find the full specs here: Redmi 4A
You can delete unwanted PICs, videos and songs. You may remove unwanted Apps.