Neck cords and loose skin: dermatologist suggested I try RF Sublative to tighten my neck and then try Botox. (Photo)

Hello and thank you for your question. Based on your photograph, you are a better candidate for a mini facelift with a neck lift.  If good technique is used,
this can be done with minimal scarring and can result in a natural look, not
over-done look, with rejuvenation of your face.  Make sure you specifically look
at before and after pictures of real patients who have had this surgery
performed by your surgeon and evaluate their results. The most important aspect
is to find a surgeon you are comfortable with. I recommend that you seek
consultation with a qualified board-certified plastic surgeon who can evaluate
you in person.
Best wishes and good luck.
Richard G. Reish, M.D.  FACS
Harvard-trained plastic surgeon

Some people require surgery to get the most improvement. There are non invasive options for improvement to the neck, which include:
botox, dysport or xeomin and/or fillers to help platysmal bandsthermage radiofrequencyultherapy high intensity ultrasoundPDO nova threads or instalift for liftingsculptra injections for collagen productionbtl exilis ultra, venus legacy, and thermi250 for constant collagen stimulationJ plasma or thermiRF internal tighteningI recommend getting a formal evaluation with an expert. Best, Dr. Emer

From a limited posted photo - it appears that you are a candidate for facelift/ neck lift.In the right hands you can certainly expect a very pleasing and dramatic result with this procedure.I would save the money and apply it toward this surgery.

Botox can be very beneficial if your neck cords are tight and standout especially when you grind your back teeth. If they are flaccid and hang down, relaxing them more has no benefit. Your dermatologist or a plastic surgeon can help you identify your situation. EXTERNAL  RF requires multiple treatments and the results are usually not dramatic. Risk of burns are much less than internal RF. 

Elena. A little Botox placed in the cords of your platysma muscle may soften your neck a bit but it will not affect the redundant skin. Also radiofrequency (RF) treatment has not been proven to cause significant skin tightening and it certainly will not tighten it in time for the wedding. Enjoy the wedding and if your neck still bothers you, consider a full facelift after the wedding.  Not enough time to recover before.  Be certain to consult with a board-certified plastic surgeon. Good luck.