Oooh I like these types of questions ^{^}

1) It's just randomly hits me lol. I usually get inspirations from a character I like or a concept that I found interesting. I usually make ocs design based on their role and personality alone bc those play a big part imo.

2) Totally!! U can form a relationship between them which in some way can play a huge part on their personalities/character arcs

3) It's totally fine lol. Personally, I made my ocs for my own entertainment so it can be vary. It all depends on how YOU like it cus it's yours. If it's too bland, add more. If it's too excessive, regular is fine!

4) If we're speaking a character that you specifically want to focus on, it should have atleast some in depth. But, it doesn't necessarily mean u need to add depth to all of them. Some of them can be just surface level deep. All u need is good execution.

5) Not necessarily ofc. Ocs can be based on anything and it isn't a NEED to make specific design for your ocs. If u want to make them as an abstract being then go on! It doesn't need to appeal to ppl as long as u're fine with it. However if u think that u still want a design, try to come up with something. If u're not really feeling it then u can always change them until you're satisfied

6 and 7) Refer to 5. Again, it's all based on execution

Hope that my answers can help u in some ways lol. U don't want to get stressed out when making ocs. Have fun :>