Your flight experience will be a hindrance, not a help, as the experience of flying the plane outside the cockpit will be completely contrary to everything you have learned. Yes you should seek an instructor.

As for the Showtime 4D .90, if you've already purchased it, put it back in the box, find a nice safe corner of the basement to put it in, and don't get it out until you can fly the snot out of a good basic trainer. Get one of the RTF models (see the sticky at the beginning of this forum on models to choose from). An aerobatic plane like the Showtime 4D will be absolutely unforgiving as a trainer and is probably better suited to a 3rd or even 4th plane. When you learned to fly, did you learn on an aerobatic plane, or a high wing trainer? Same principal applies. Learn to fly the basics with the tool designed for that purpose.

As for the radio, if you go with the RTF, you can always purchase another radio when you're ready to move up to larger aircraft. The JR 10x PCM is way more radio than you need at this point. Get a good 6 channel Computer radio (such as the HiTech Optic 6), and you'll have plenty of radio for the next 2-3 years while you're improving your skill. Most of us have 2-3 (or more) radios anyway.

Brad