Buy some 25 or 28c tires, lot of love for Continental GP4ks2 on the road machine. Or Continental 4Seasons - I run the GP4ks2 on my front and 4 Season on the rear.

New bar tape, new cables and housings, replace other consumables if needed.

Have the hubs greased and cleaned. Then that's it. Spend your extra $600(?) budget on some clothes, clip in shoes and pedals. Maybe buy a Claris or *Microshift* group to go with brifters instead of DT shifters? I probably wouldn't though.

Don't overthink/over spend on these, just maintenance and ride.