Ditto on what the others have said. A good fitting goes a long way. And don't think, "Once fit, always fit." As you age, your body changes enough that you can expect to have to make minor and or mild adjustments. Also, at over 300 lbs., your body will definitely go through many, many changes so expect to be refit a few times.
As for your spandex question, they're actually bibs or bib shorts. Don't make the mistake of only getting spandex. Your buttocks will most assuredly appreciate your investment. I ride the older Sugoi RS bib shorts. Many people have their individual preferences but I have had great results from the Sugoi RS. Also, invest in some chamois cream. It'll help with the inherent rub and friction that comes with increased miles. The Assos line is nice, although a little pricey. The Utter Butter is highly recommended and far more affordable.
Make sure your saddle is the right saddle for you. I went through four different ones before I finally settled on my Fizik Arione which I later replaced with a Fizik Aliante.
As for increasing your miles, my only advice is ride, ride, ride. When I got my first ''real bike,'' I squeezed out 12 miles and my butt was killing me! Now I ride 50 with no discomfort at all. I've ridden several Centuries (100 miles) and try to ride a Metric (62.1 miles or 100 km) each time I ride. Practice literally does make perfect.
Ride safe! And welcome aboard.
| current weight: 204.8