Below are the best times for visiting the trio that you've mentioned for wildlife spotting specifically:
Kruger - July to September (this is the cold/dry season and so there is less vegetation, making wildlife spotting easier)
Hermanus - July to October (though whales are there from about May to December)
Boulders Beach - February to August (Feb-Aug corresponds to the breeding season when most penguins are on the beach, whilst Sep-Oct there are least penguins around, however the colony is there year-round)
As you can see it's not easy to get all three wildlife peak times to coincide, but generally you're looking at July and August as being the best. However please also note that this coincides with the southern hemisphere winter, and therefore temperatures are lower than at other times of year and on the coast around Cape Town this is also the wettest time of year.
With regards to adding another solo South Africa departure in 2020 after the 7th of October, as things stand we do not plan to have any more departures until early 2021. Whilst that may change if demand is high it is not something we can guarantee at this stage.
I hope that helps,