Separate ticket questions
 

Good morning all,

Our family of 5 is looking at the following itinerary:

USA-LHR then 5 night stay in London
LHR-JNB on BA55 landing 0700 on A380 (familiar with A380 issues).
JNB-VFA on separate ticket, most departures at 1130ish.

HRE-JNB on separate ticket, best departure at 1330 landing JNB at 1515
JNB-LHR-USA either BA56 (1925 departure) or BA54 (2110 departure)
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My understanding is that if we have carry on only we can move through the transit area without having to clear customs and immigration and that transfer is very quick. If we check bags we have to clear immigration and recheck our bags which can take quite a long time. It would be really handy to be able to check our bags in London so we aren't having to deal with the luggage all day before the 1900 departure.

With the scheduled 4+ hour layover would we be okay checking bags, especially with the A380 issues?
Should we keep the intra Africa flights separate rather than a multicity ticket incase we miss the first JNB-VFA flight?
Is it better to try and get on the earlier JNB-LHR BA flight or does it matter? Is it more reliably dispatched? Both flights will be A380s at this time.

We have trip insurance that will cover the missed connection as long as we have 3+ hours scheduled between the flights.

I know these decisions will depend on risk appetite. I'm trying to understand how risky each of the options are.

Thank you