It can be a bit chilly out on the AM and evening game drives, we both had a lightweight fleece which came in handy although we never found we needed the fleece AND long trousers really. We were inside the van with a pop up roof so as long as your arms/top half isn't cold the rest of your body is usually OK.
I had a 'wrap' for the evenings in the lodges (to use over short sleeved tops) and a long sleeved muslin top but didn't really use either, hubby was fine in a short sleeved shirts.
Your safari luggage should be in soft holdalls, you'll find everyone interprets what they think is the correct 'size' differently. Just take what you need - it won't be all that much anyway so it'll be difficult for it to be too big - unless you are on a flying safari, in which case the holdalls mustn't weigh more than 15kg.
I have to pinch myself to believe I've just had the most fantastic holiday of my life.........Enjoy!