It is likely a general contractor would be the best fit for this project. We don't charge for bids. Where are you located? And a good general contractor will handle this project and maybe sub out things that aren't their area of expertise.

Are you changing out the flooring at the same time? If not, you will probably want to make sure that the current flooring runs under the existing vanity and will not be damaged during its removal. My vote is for a GC rather than a plumber for this. The GC will be able to help you with the damage to the wall, baseboards etc. that will occur when you change this out.

If you are very experienced at this should not be a problem. However, if you are not to avoid a leak/flood I would hire a professional since you have an exposed area below the new vanity and prior you have a enclosed vanity so where does the plumbing sit? Depends on where your plumbing sits, age, etc.

In my area you'd wait a very long time to get a general contractor to bid on a job this small. Christmas if you're lucky. I'd feel comfortable hiring an experienced handyman in this case. Try Angie's List.

A GC would be the best bet for you. You will also need to remove countertop which runs all the way to above the toilet as well as the 4" (am assuming) backsplash which means that you might need some drywall/paint repair as well as possible flooring repair as mentioned above, not to mention the mirror.

Also as Porter Edun mentioned above, depending on where plumbing is located, and how old the pipes are, you might need to do some other plumbing work as well.

I would say no, but inspect the plumbing lines and valves. they may need to be replaced if they're old. but not a big deal. A simple 'how-to' on Youtube may be all that you need. Now if you need to move the lines, or redo the drain or something along those lines, then call a GC or local handyman.

I can't answer your question without knowing your level of DIY skills and your tool selection.

Very basic plumbing skills required, if your fairly handy it is such a small project would be cheaper to have a go yourself, can recommend a very good guy for a decent rate

I do believe, your problem can be easily solved without a professional plumber, but if you are not sure that you can handle the job or you might do something wrong, then call a special service that can help you, in my opinion the right solution is to call such service. Although also I will say that it is very easy to replace everything without plumber. In general, if you really stop at ordering yourself a plumber service, then I can advise you water heater installation Vallejo, a service that can help you with your problem. The service is of sufficient quality and can do its job quickly and well.