Is getting rid of gnats outside a job i can do myself?

yes, nothing here needs a pro. outdoor gnats are breeding in something damp, so go looking for it: soggy mulch, a blocked gutter, a bucket or plant saucer holding water, overwatered pots on the patio. dry those out and the numbers drop within a week or two. for sitting outside in the evening, put a fan on the patio. they're weak fliers and a bit of moving air keeps them off you better than any candle.