help getting started

 so i got a really limited knowledge about anything web related so bear with me.  Im trying to get a contact form up to start taking leads for my repair service while i try to get the rest of this figured out, but the service is slightly more complicated than the standard options of the generic form allow for.  at least for me to do neatly anyway and not only that but ideally i would like to start recording the customer info and equipment data so that when the customer logs in they don't have to input the info back into the contact form again.

so far i think I've figured out how to assign custom fields to the customer data, or at least I've found the section explaining it.   i can also, thanks to treehouse, build my custom form out of html and basic javascript so that some of the service options hide until needed.  but what isn't clear is if and how i can get the data from the form into the customer profile and back again.  

do i just use the merge codes for the field in side my form?  if thats the case, how do i allow for multiple saved vehicles to be cycled through on the contact form, use a dropdown menu containing the merge codes?

i also read in the custom form section that the entire page is a form in itself, and it has me wondering if rather than making a custom form, i couldn't just write the inputs to the page, using the various custom widgets such as the tab to my advantage.

would it be possible to put a button at the bottom of the page to generate a list or screen shot of what the user has input along with the contact and equipment info?  would the custom field data be able to be stored for the contact and equipment sections this way?

I'm going to include a part catalog later on another page, so being able to have the customer info/login and equipment sections display in the header would be awesome. i realize this is a lot to process, I've been up all night searching through the forums and support for the answers myself.  any advice or direction on what else i need to look into would be appreciated