They are not an animal you should get based on whimsey, they are animals that take a lot of effort and time to take care of, even if compared to some other farm animals they’re considered lower maintenance.

Donkeys are working animals, but I don’t know what you mean by farm labor exactly. They were primarily pack animals and transportation animals. They helped people carry their stuff when travelling because they’re actually quite strong, often stronger than horses of comparable size, and they’re lower maintenance and less expensive than horses. Even today they’re still regularly used for that purpose in countries with less industrial development. But even in countries where they aren’t used as pack animals donkeys usually still have a job of some sort, often as a comfort companion animal for other species like horses (they’re less high strung than horses and have a calming effect on horses that take behavioural queues from herd mates for example) or guardian of a herd of other livestock like sheep or goats. They aren’t made to stand around doing nothing in a pen all day. And no, you absolutely shouldn’t just leave one alone for 3 days, they’re highly social animals who need companionship to be happy. They can get lonely and bored easily, and will not enjoy being alone for long periods of time. They do best with a herd to socialize with or at least another donkey (with some caveats in regards to ungelded donkeys). Companionship is very important for their mental well-being, and no, you will not be enough on your own, especially if you plan on taking 3 day fishing or shopping trips. Donkeys often form pairs and bonds with other animals in their herd and being without their companion or companions is stressful for them.

And they may be easier to care for than horses, but that doesn’t mean they’re maintenance free, or expense free. They are high maintenance and expensive animals to keep, just like any larger animal. Their hooves need to be clipped regularly, they need constant shelter available since they have less protection from the elements due to the fact that they were bred for arid environments. They need proper access to grass hay for grazing but not enough to cause founder and obesity since they’re prone to over-eating if food is available in too much abundance. They need a certain amount of grazing hours per day, and constant water available. And those are just the very basics, not even including stuff like vet costs and vaccinations and grooming. I could go on for much longer on this topic, but this comment is already getting long so I’ll just say there’s a lot involved in their upkeep.

Donkeys are also not easy to train like horses tend to be, and they can exhibit a lot of stubbornness. There’s a reason they aren’t exactly known for their obedience. They also need a lot of enrichment via toys and activities because they’re intelligent animals who require regular mental stimulation.

I wouldn’t consider donkeys to have almost human lifespans. They live to about 30-35 years on average, which is a larger lifespan than some pet species, but isn’t comparable to humans.

If you want a lower maintenance companion animal with lots of personality then tbh just getting a regular dog or cat would probably fit your intended lifestyle more. You can even leash train them and bring them on your trips if you want. Or if you want a longer living animal, then get a tortoise or something, they can have plenty of personality and live a long time. In all honesty I don’t think a donkey is a good match for you or your intended lifestyle. Only people who have significant experience working on farms and with farm animals should ever consider getting something like a donkey. They aren’t a beginner animal by any stretch of the imagination.