Learning the basics of the job didn't take long. If you either know or can easily learn anatomy (especially the locations of arteries and veins), it isn't that difficult to pick up.
To do basic embalming, it takes some practice. In mortuary school, we embalmed ten bodies, and that was enough to do a very basic job. The more advanced things, such as specific cases (dealing with odd types of death - strangulation, morbidly obese, drowning, etc.) takes some learning since not every body is the same. There is no set time frame on how long it takes to learn such a craft.
Once the embalming is done, cosmetics come next, and unless you are already good with them, it can take quite a while to learn. As a man, I never touched cosmetics other than Halloween, and suddenly I had to present a person complete with perfect makeup. I'm still not great at this part, but I'm learning.
I'm not sure if you are looking to combine both and run the entire event or just prepare the deceased for viewing. As an embalmer, the benefits are mostly that you get to continually learn since no two bodies are the same, and you also know that you are involved with having a grieving family getting a good chance to say goodbye to someone they love for the last time. Negatives for an embalmer are that sometimes bodies can have very foul odors, depending on the circumstances, there may be complications that are difficult or impossible to overcome, some cases are bone donors which takes a LONG time to embalm properly, risks of disease from the bodies, risks of cancer from the formaldehyde, risks of being very messy due to the process and the condition of the case, etc. To me, the benefits far outweigh the negatives.