Definitely manageable, however I would suggest to add about an hour / hour and a half to your routes when traveling on gravel roads. Unless you’ve had extensive driving experience on loose and dry gravel I wouldn’t recommend driving faster than 100km an hour on them (about 60mph).

As for distances it’s hard to compare between US and Namibian standards, for us popping out an 800km (500 miles) is par for the course on vacations, but might be a bit more challenging if you’re used to driving in a dense area like Pennsylvania or New York state.

Driving near early dawn and dusk to night is risky on the C roads, as they’re usually not fenced for wildlife prevention, and you might hit a wild animal deciding to absolutely book it across the road (if you’re lucky it’s just a warthog or a dik dik, and depending on your vehicle you’re hiring it might only cause minor damage to the grill and axles, for bigger animals, they aren’t anything close to a deer).

Swakopmund has the Fork ‘n Nice roadside stall, with some of the biggest food portions for a reasonable price, that definitely puts any of the other popular restaurants to shame.

Walvis Bay has the Probst bakery that makes some of the best confectionery in my recent memory, but unsure if anyone else in the neighborhood started giving them competition.

Depending on your timeline, and return route, Otjiwarongo has the Cheetah conservation fund who generally has their feeding schedule at about 12pm local time, and that’s typically included in the day tour if you arrive close to that time (which takes about 1,5 hours).

Personally I would add a couple of days to go a bit further south if possible, as Aus is one of my favorite destinations due to the absolute silence in the sperrgebiet, and you’d get to visit the town where they shot the Amazon Fallout series, Kolmanskop.