In the name of God, Most Merciful, Most Wise.
are there any limits I should have as a muslim with my non-muslims friends ? Should I consider them to be "friends" or there are islamic rules to call someone "friend" ?
Yes, there are limits on having disbelievers as your friends.
Here are the conditions on having disbelievers as your friends.
1) as long as they don’t mock, insult or make fun of any elements of Islam.
2) as long as they don’t treat you bad just because you’re a Muslim
3) as long as they are not against Islam.
And remember this, also prophet Muhammad made a Christian girlfriend, then they got married, then laster on, she turned as a Muslim woman, so yes, you can be friend with anyone you wish, either with atheist, or anybody, but you have to be wise, and chose carefully whom you select friends, because there are some who are jerks, and they make fun of any element of Islam, this kind of friends, you leave them, and find another friends, unless your previous friends wishes to ask forgiveness from God because they have mocked, insulted or make fun of any elements of Islam or they went against Islam, then you can be friend with them again, but if they still, then leave them and forget about them.
Hope this is your answer you’re looking for, and if there is anything wrong on my answer, just let me know.
And God knows best.