US Citizen sending money overseas

Is there a limit on how much I can send? Can I send $100K plus?

No. Yes.

What is the most appropriate way to send money - international wire? Is there international-wire limit restrictions I need to be aware of?

Yes. No.

Is there any tax obligation should I be aware of when sending money home?

If you're a US tax resident (which, as a US citizen, you are), you should be aware of gift tax rules. You'll probably want to talk to a licensed tax adviser (EA/CPA licensed in your state) and/or attorney, to understand the ramifications in full.

If my family can return my money back in future, great, if not I really don't care, but when (if) I get my money back, will I have to pay taxes on bringing my own money back into US?

No. But if you're giving it as a loan - you'll get paid interest which is taxable income to you.

Is there anything else do I need to be aware of?

The rules of the country which you're sending the money to.