9 days on bicycle between 2 oceans, across Central America, on highways, backroads, and offroad. See posts: part 1, part 2, part 3, part 4.
Being completely self-reliant means more luggage and more weight (slowing down the bike considerably), and does not pay off in these circumstances. There are a lot of "cabinas" (unexpensive hostels) everywhere, so the trade-off of speed and comfort for self-sustained living is hard to justify when staying so close to civilization. Despite that, it was a good exercise.
Buying a bike vs renting a bike: about the same price as primary investment (rent prices are extreme), however renting a bike means that it's been tested and maintained in a good way. I had no chance to check how easy it is to sell a used bike, but given a time margin it should definitely be possible, and would return a part of this investment. A few people fly their bikes from their home counties, should be the best approach.
Bringing spare parts and repair kit is essential. Apart from flat tires, all kinds of reparations might be needed. Chain oil is necessary after river crossings. Brakes will be used and will need adjusting. Make sure the bike you are getting has pannier racks, and bing your own quality helmet and possibly a lock. Bring the best lanterns you can, and avoid biking by night.
Gear is all. I would not have made it without my modular backpack, which I redesigned to form saddle bags and fit the rest of the gear into. A good mosquito spray is essential, I usually buy local so I get a targeted one. A water bottle with a built-in filter basically saves your life - Costa Rican tap water is normally potable, but it might be a long way between the taps, and in direct sunshine and over +30 C you might dehydrate so much that a fill-up from a nearby waterfall is needed. Bringing water along means more weight, means more work, means more hydration lost. My portable stove did a good job, also the light-weight tent and an inflatable mat. I did not use a sleeping bag, only a liner. That was OK during most nights, except when it rained so much that the tent and all the gear were inspide and out, and the high elevation made it chilly. I had to knock on a door and borrow a blanket in order to regain some warmth.
You gotta have good cycling gear, that's clear, including a helmet and cycling gloves. A UV-colored shirt is a must, so cars and trucks will see you - even locals wear them. Sunscreen is expensive, bring a good one - also glasses to protect from both sun, bugs, and mud splashes. I also used a bandana over my face when it was wet - knowing the amount of roadkills and other nasty stuff in the mud, it's not the splashes you want to get near your mouth. A waterproof phone, and drybags for everything else is recommended. I bought a whistle to use in urgent situations, helped a lot against the aggressive stray dogs. And most of all, I thank science for sports tape, which I could apply to my back parts and thus not need to endure the pain of chafing against a bike seat for 9 days straight.
Thee were some dangerous stretches, and it's a good thing to know about the risks and try either not to go there, or to manage the risks actively.
There are no maps to buy in stores, but some hotels have overview maps, at least for the roads. After a while (and a few unnecessary detours), I started to download offline maps to my phone, and use the GPS function to doublecheck where uncertain. I have no bike GPS, and happy to avoid that frequent charging of yet another device.
Also, a good guidebook and an open mind always help to make such a journey a good experience.
(This is the sum-up of adventure description, which starts here.)