@Danny Sok
Danny, when I started out, I commingled my money. Just like you, my money was the rental money...my credit card was the rental credit card. Also like you, I did keep the Security Deposit separate from all other funds. So long as you are able to account for what is a rental expense and what is a personal expense you will be okay. In the end, it all goes on your tax return anyway. It will get more difficult as you grow, and generally it is a good practice to keep you personal money and rental money separate.
Today, I have a credit card that I use for all rental property expenses. I expense against each property separately to keep accounting clean. I also have a single account for rental income that pays all mortgages, utilities, fees, etc. What is left over I keep. With that, I do have a reserve built up for each rental property, which took some time to build. But now, I get to keep the profits and manage the process.
Depending on your state, there may be certain requirements on where you can place certain funds (like security deposits). In the end, how you manage your business is up to you. There are several way you can cut it, and everyone will have an opinion, but do what works for you and change when you need to.
I hope this helps!
Nick