My questions are:

Can I apply for status change before my H1 start or not

-->Yes........you can change your status anytime from one status to another.

Can I change my status from h1 to F2 since my girl fren is in Student visa?

-->You can change your status from H1 TO F2 ......it takes about 3 months and you need to contact your international office ..........but you are not dependent of your girlfriend...........you need to be spouse .....that is you need to be married (and NOT BOY FRNS/GIRL FRNS)

What will be the Documents for changing H1 to F2 status?

-->Contact your International Office ..........they will take care of eveything.........it is I-139

How long will it take to change my status from H1 to F2?

-->It takes atleast 3 months

My employer (dhoti Company) does not provide me anything for this matter so do I need any documents from them or not?

-->You don't need any documents.............just take your approved H1B docs to International Office

I have my H1 approval soft copy so will that be ok while applying for the F2 or do I need original one?

-->Yes.........soft copy should be fine .........as far as you have your case number..............but some Int Office might ask Original.................if so go to your current employer and tell them that you want to change your status from H1B to F2................they might ask some trainning fee etc

If I apply for the status change from H1 to F2 and before the approval of F2 what will be my status? Will I be out of status?

-->You will be in H1B status until your F2 status get approved

If my F2 status is not approved what will be my status? will I have my H1 or will it be terminated after I apply for the status change?

-->There is 100% gurentee for your F2 status approval if you submit proper docs like marrige certificate etc