Don't know when your trip is, probably past already.
I am not a professional, just a camera user.
I have both the Panasonic 100-300 and the 100-400, use either on a G80 or a G9.
The 100-300 is light, easy to use and carry, easy to hand shoot with. It fits in a standard "long nose" dSLR case to carry around.
About third the price of the 100-400 (
second hand)
If you don't use one now, you are quite likely to enjoy it on your return.
The 100-400 is much heavier, more bulky and harder co carry around, however used with the G9, you get the benefit of dual stabilisation (check which lenses do the same on Olympus) which is a great help in low light as long as the subject is not moving.
It is easier to use on a tripod than hand held, hand held at 400 my success rate is about half that of using on a tripod (probably down to me, others will probably do better)
It is sharper than the 100-300.
If you don't use a long lens now, maybe less likely to enjoy this on your return.
Daytime light is likely to be less of a problem there than here, having lived most of my life in Africa, you really notice the lack of it here
I'm told Panasonic M43 lenses will work Olympus and vice versa, there are certain functions that do not, like dual stabilisation, I don't know from experience as I haven't tried.