Go ahead. Buy the plotter. It will work fine. Get some 10 yard rolls of vinyl and a roll of transmask tape. Buy a sign making computer program and learn how to use it (it will likely run fine on your existing computer). Buy some font licenses (or steal some online, they are availble but with no license to use). Get a few extra rolls of vinyl because you will screw a lot up when you are learning. Make sure you have a big, flat rigid table to apply your transmask (trapping air is a *****). Learn how to set your plotter blade for accurate weeding, and practice weeding for a while until you get the hang of it (once vinyl sticks on something, it is done). Make sure you have air-conditioned space to store your vinyl, and make double sure you vacuum and dust before attempting to cut, weed, and mask your vinyl (you will be in an airconditioned space, so it should not be a problem). Make sure you use the right vinyl for the job (cast, calendared, hi-tack tape, low-tack tape, etc.).
Or order your cut vinyl from a local shop and save several thousand dollars and several weeks of time.