Learn English – “cross one’s mind” and “enter one’s mind”

Notice that in your own examples, you vouched for a person, but guaranteed an action. This is exactly how I'd use these words, and it does seem to reinforce your intuition: "vouch" is about a person's character; "guarantee" is about actions or things. We might also say, however, that "guarantee" emphasizes the future, while "vouch" emphasizes the past. To explain my position, I'll call on the Oxford English Dictionary.

Guarantee

The OED lists the following meanings for the verb "guarantee":

1. To be a guarantee, warrant, or surety for; spec. to undertake with respect to (a contract, the performance of a legal act, etc.) that it shall be duly carried out; to make oneself responsible for the genuineness of (an article); hence, to assure the existence or persistence of; to set on a secure basis. (Example: "Written languages guarantee a systematic pronunciation.")
2. To engage to do something; to warrant or ensure that something will happen or has happened. (Example: "I'll guarantee that he'll never return to Bengurry.")
3. To secure the possession of (something) to a person, etc. (Example: "Christ guarantees to the faith of His brethren...a true quittance and defence from sin.")
4. To secure (a person or thing) against or from (risk, injury, etc.); to secure in (the possession of anything). (Example: "Angus was strongly disposed to make the attempt, if he could be guaranteed from loss.")

All of these definitions and examples state that something will happen in the future, or promise to do something or cause something to happen. In the first example, "Written languages guarantee a systematic pronunciation," the claim as I understand it is not that written language can't exist unless a systematic pronunciation is already in place; the claim is that written language tends to create a systematic pronunciation because we come to associate certain symbols with certain sounds. (Obviously, this claim would not apply to all writing systems.)

"Guarantee" is also often applied to products ("We guarantee this vacuum cleaner for life"); again, this is a statement about the future: the vacuum cleaner will not break down, and if it does, the manufacturer will replace it.

Vouch

"Vouch" has quite a few meanings, many of them archaic and/or specific to the legal realm. "Vouch for", however, has only these three:

1. To speak or bear witness in behalf of (a person); to be surety or sponsor for. (Example: "I dispute not the lad's qualities, for which your reverence vouches.")
2. To supply evidence or assurance of (some fact). (Example: "The certainty of the law...is vouched for...by the results of experiment.")
3. To give personal assurance of the truth or accuracy of (a statement or fact). Also with accuracy, truth, etc., as object. (Example: "I love the country better than ever, I can vouch for that.")

I take it that the first meaning is the one you had in mind. My belief that "vouch" emphasizes the past, rather than the present, rests on the fact that even though you vouch for a person with an eye to the future--securing a job for her, for example--you're vouching for certain qualities, like character, experience, expertise, or personality, which are already possessed by that person. You're not guaranteeing that you'll take over the job if she fails; you're just saying that she has the expertise and background necessary to succeed at it.

The meanings of the two terms largely overlap. Frankly, when they are used together, I think it's pretty much a redundancy for emphasis. If you asked a salesman, "What are the most important features of your product?" versus "What are the most important features and characteristics of your product?", I would expect you would get the same answer either way.

We do this a lot in English. Sometimes a single word just seems too abrupt. So instead of saying, "When the letter arrived, Sally was happy", we might say "When the letter arrived, Sally was happy and joyful." Instead of just saying, "Bob is irresponsible", we'll say, "Bob is lazy and irreponsible." Etc. Sometimes the extra words arguably do add some shade of meaning, but often people add extra words that mean pretty much the same thing just for emphasis: instead of saying "she was very very happy", it sounds more literate to say "she was happy and joyful".

You wouldn't normally talk about the "features and characteristics" of a person. This is a phrase used to describe inanimate objects, usually some machine or gadget. If you asked, "What are Mary's features and characteristics?" it would sound quite strange, like you were describing here as a product that you were going to sell.

When talking about a person, "features" means his physical appearance. If someone asked, "What did you notice about Charly's features?" they would expect an answer like, "He has brown hair and a scar on his left wrist." Similarly if you ask about the "features" of a place, like, "What are the features of the Toutle River Valley?", they would expect you to describe physical (geographic) features, like "There's a hill on the north end, a deep gorge running most of the length," etc. But if you talk about the "features" of a product, you normally mean details about how it functions. If someone asked, "What are the main features of your new Whizbang 300 cell phone?", they wouldn't expect you to answer, "It's black and sort of rectangular", but more like, "It has a built-in GPS and a function to mask out background sounds when you call your wife from the bar."

If you talked about the "characteristics" of a person, that could mean anything about him, from "He has blue eyes" to "He is an excellent basketball player." I suppose you wouldn't use "characteristics" to describe something very temporary, like "He is sitting at his desk"; it would normally be used only to describe a fairly long-term attribute.

(Whew, that answer was longer than I intended.)