I am really to file my first Form 1. My question is do I need to find a class3 dealer to file it for me or I can file it by myself? If I can file it by myself, does anyone knows who will sign the form in Houston(Harris county), TX? Thanks in advance.

Are you building your own SBR/S, AOW, or supressor or buying it?  The form 1 is to build and NFA weapon yourself - YOU are the manufacturer.  If you're just buying one thats already made & registered, you need a form 4.  

If you're going to build it yourself and are doing a form 1, you do not need to go through a C3 dealer.  Do the form, send it in, wait for approval, build your piece.

You can also buy directly from another ownwer on a form 4 if the other guy (the seller) is in your own state.  If the seller is in another state, you have to go through a C3 dealer.