Haters are gonna hate, nothing you can do about them. I applaud your decision to change your fitness lifestyle, cycling is awesome! I am sorry you had a bad experience though, jerks are everywhere. I am not familiar with vintage bicycles, so I am of no help there, but I do agree that taking the bike to a competent mechanic is the way to go just to ensure the bike is safe and roadworthy.
You didn't state what your ultimate fitness goals were, are you looking to loose weight or just build up stamina / endurance. There are a bunch of us who have lost a lot of weight and we can help / coach you if that is your plan. I personally have lost 90 pounds since Sept 2014. I will always be a Clyde because I am 6'2", and I am still teetering on the 200 lb mark but my fitness level compared to a year ago is crazy. I lost the weight primarily by counting calories without much help from the cycling. When I plateaued at 80 lbs down, I began riding in earnest (April-ish this year). Over 350 miles in June, 440 miles in July and already 102 miles this month. Still losing inches currently, leaning out but no weight loss to speak of lately. I'm OK with that
