Lots of questions ... all important. I can only suggest ideas on a few things:

Medical Evac: try HUBB sponsor Global Rescue, also Med-Jet Assist. I have not used either, but many travelers have, read the reports.

Credit Cards/Money: You will need at least 2. Also, 2 or 3 ATM cards. Use ones from different banks/networks to cover all the bases. Often your card WILL NOT WORK ... no reason, it just won't work. So try another card.

You can draw CASH from ATM's ... if the machine recognizes your card! Some businesses won't take credit cards so, get your cash from ATM and use that.

Try to use Credit Card with NO Foreign transaction fees. These are killer and add 2 to 3% onto every purchase. ATM's almost always have fees ... hard to avoid. I usually draw LARGE amounts of cash at one go. (usually about a $3 fee) Be sure to cash out before crossing borders.

Cell Service: I'm weak in this area, but I think you need an "UNLOCKED" phone and then you will need to buy a local SIM card for every country, then contract with a Verizon affiliate, OR ... buy a local, cheap cell phone in each country.
Everyone has a cell phone now.

Internet Access:
In towns big and small there is Wi-Fi available. In remote areas not so much but even this is in flux. More and more cell towers everywhere. Even in jungles and deserts. Even if you can't get WiFi your SPOT meter will show where you are.

El Salvador:
I hadn't heard of any recent problems in Salvador. But if you must ... you can easily ride through in a few hours. I lived in La Libertad (Surf Spot) many years ago. Lots more violence going on in Mexico these days. (Cartels vs. Army)

Search & Rescue: Spot (you need one!) Allows friends and family to track you and alerts when you set it off if you have a problem. Good reports on this service.

Medi-Care: Many countries have FREE health care ... even for foreigners. But far as I know Medi-Care does cover some of your out of country medical costs and your supplemental should too ... check with them to confirm.

I like your idea of storing bikes then returning to ride more. I would ship your KTM from Colombia to Florida. Quite a lot of cargo goes that route. Expensive but not crazy. Either air or sea.

Good planning!

This planning phase is stressing me out! Yes, I have a Spot. Your info is appreciated and the wife and I are reading it over and over. There is a guy on Facebook that I've been chatting to also, he's on a bike like mine and has been very helpful. He's using a Schwab card (never heard of it). He said to have my phone unlocked and buy SIM cards as there only $5 or so.