Firstly, August is a good time to go to the Kruger park as it is winter and the day time temperature a bit more bearable than in mid summer (December). Also, winter is the dry season, so the vegetation is a bit reduced, making it easier to see into the bush; in summer the grass at the side of the road grows quite tall and can restrict visibility.
As for the amount of time you need to get around the park. It is big and the speed limit is very low - 40km/h (25mph) (see https://www.kruger-national-park.de/pages/english/travel-guide/wildlife/tips/regulations.php), so it takes a long time to get from place to place, so you'd need almost an entire day to cross the park. There are other restrictions, example driving past 5pm is not allowed etc.
Thinking about the time you need in the park. The best time to view game is early in the morning and towards the evening. In my experience you can have days where you see very little after driving for 8 hours and other times you see a lot in a short 1 hour drive, so spending a week or more would be better.
Regarding hiking trails. Hiking is prohibited. You are also not allowed to exit your car unless in a marked area and it isn't recommended putting your windows down either (see the link above). However one of my best experiences has been on a guided game walk - this can be arranged wherever you stay.
Finally accommodation, this is very subjective, but a lot of it is self-catering (fully kitted out kitchen, but you provide/bring your own food) and needs some good organisation. Each camp site also restaurants and small shops.