Greg, You’ll wear your arms out long before you get rid of scratches or other blemishes. If your gel coat is thick enough a random orbit polisher with different stages of cutting pads and media will take care of it, just really be sure it’s a random orbit or you’ll risk burning paint. If this is the only car you’ll need to work up, the cost for the equipment will be more than a good detail guy will charge.
How much did your detail guy want to charge and did he promise not to go though the gel coat?