The real question is whether this is a good enough bike for what you want to do. Is the gearing appropriate for what you have in mind ( and a trailer will require lower gearing still). How comfortable are you on this bike that is 20 years old, do you still fit it as well as when you bought it.
Another isssue is whether this is a solo trip or not, are you setting the pace, or someone possibly differently equipt.
Obviously there are many people in developing couintries traveling long distances or with heavy loads on very cheap bikes. They may not worry about walking hills, or the quality of the experience.
Doesn't sound like what you currently have is a touring bike, and if you want to move in the direction of a touring bike then you can probably do better by putting the money into something other than a YAK. Many people like them, but most people still run pannier on a touring geometry frame.
Do you won approapriate camping gear? If this is just a one-off, then maybe you should put the money into a credit card tour.
My feeling about training is that for a solo ride with the right gearing you hardly need to train Obviously there are routes where traning will be necesarry, basicaly depending on the amount of climbing. I just get on the bike and go at a comfortable pace.