Is it safe to send to my own address from my wallet? I have a wallet.dat which has so many addresses in it. Like 1, 2, 3, 4, ....., 1234324234 addresses. (Each number is address)

I backed up original wallet.dat, and I want to use this light wallet.dat from now on.
This light wallet.dat has only 1, 2, 3, .... 100 addresses in it I think.
(keypool size was 100)

Both wallet.dat has same address "1", so is it okay to sending all coins to address "1" and use light wallet.dat after that?

It may cause sending to address "1" from "1". Is it okay?
I think you need to understand a lot more about public and private key cryptography first. It sounds like you have no idea what the address actually is or how it's used in Bitcoin.

Yes, the standard client does generate addresses in advance, and these are used by the client when you request the "creation" of a new address. But if you (or rather your client) does not know the private key associated with the address, you will lose your bitcoins forever.

Therefore you need to know both the address that you are sending to and the private key, to be safe.

Can I recommend that you learn about your wallet and how it works by using your bitcoin client in testnet mode first.