Sorry for the long post – instead of replying individually, I put everyone’s together!
Thanks so much for all the suggestions – I am glad there are several weeks yet before we leave so I can consider everyone’s input. Thanks for everyone’s concern that I take good care of my wife. That is my #1 priority…as many older and wiser men have said “A happy wife = A happy life”. I am thankful to have been married to my best friend this long and am being careful not to let a hobby endanger that. This trip is still a surprise to her – and I assume it will remain a surprise, as she has never been interested in reading an online photography forum!

HDNitehawk – Thanks for the input, I had not considered renting the 300f/2.8 or the other lenses, it is definitely something to check into (I have never rented a lens so am a little apprehensive to break myself in on this trip!). You are right about the overlap in the 70-300 and 70-200. Maybe I should rent the 70-300 and leave the 70-200 at home. Good point on the macro too – my “macro” is probably more accurately “close-up”…I don’t have the rails and ring flashes, etc. – I just like the IQ capabilities of the 100mmL handheld.

Joel – Thanks, you are right about the 300f4 – that has been my favorite for birds (60D-300f4+1.4vii) so I tend to bring it along more than I need to. Bringing the 60D body along is great for close-ups too. If my 1.4 extender worked as well on my 70-200 as is does on the 300 – I would probably sell the 300…but for some reason, IQ of the 1.4ii disappoints on the 70-200 (but the 2.0iii extender is great on that lens). The difficulty for me is when I use the 70-200 2.8 with the 2.0extender – the whole setup is very heavy and unwieldy. After holding that for a while – the 300-1.4 combo feels like a breath of fresh air!

David – I appreciate your comparison of the 70-300 and the 24-105. I am now considering renting the 70-300 (maybe leaving the 24-105 and 70-200 at home). The 8-15, 40mm, 70-300 would be a compact option.

Brant – Thanks so much for sharing pictures from your trip, and also the very helpful tips. I am checking into the CPL and ND filters you recommended (there seem to be a lot of options!) – I am not very experienced with them, so it will be a great opportunity to learn (without adding too much weight to the luggage!).
I appreciate any insider suggestions on tours from you and your brother-in-law. Hopefully we will be able go on a couple tours, we won’t be leaving for several more weeks (early October) – look forward to hear how their trip goes, and any other travel info you would like to share! One that looks interesting is the “water safari” type tour – it looks like you might be able to get fairly close to the wildlife along the river, from a dry, shaded boat.
Using the Speedlite for wildlife will come off the list – thanks! Some of my favorite pictures have come from the 100mm – but you are right, when I travel with it – too often it never comes out of the bag. Since I have a bad habit of NOT using a tripod – your reminder to take that is helpful. It sounds like once you go to Costa Rica, you start planning your next trip when you get home!

ahab1372 and jrw - Thanks for the suggestions! Maybe I will try to keep my face in the camera on a photo walk, only when she is enjoying the SPA

Brian – Thanks for the suggestion – you are right, my only concern with the 70-200 is the weight. Based on the ISO charts I just struggle with the 70-300 compared to the 70-200 IQ – but I see so many awesome pictures from it, I really appreciate real life input from experienced users like you.

Thanks again to everyone – since I have a really busy schedule between now and when we leave, it is helpful to have the experienced input from all of you. It will save me a lot of time when I start packing – and has given me many great things to consider that I had not thought about.
Brian