Looks like a nice bike. Changing wheels and or tires is the biggest single improvement you can make, also most $. Confirm but looks to me like your rims are 17mm inside so according to Tire Sizing Systems 28mm tires will fit. I'd do a search to see what people are using. Way different ride.
Your crank's biggest gear is 42, for probably $50 you could get taller gears, maybe a 48.
Flipping the stem would get you down more, less windage, better power, if it's comfortable.

and welcome!