As I am a non native speaker I appologize for the indulgence of giving my 2 cents and I warn that my grammatical understanding might be tinted by german synthax. But iI think that I am able to help, or atleast to point in the right direction. As it was already mentioned you would have to change "has led" to "have led" in your original quote if you would apply "and" instead of "together with" and i. I believe this to be the main issue here. Together with is no "Linker", it is a preposition which normally introduces an adverbial phrase. As it is no conjunction (further down the explanation why and how exactly it differs from "and") the conjunction-reduction is neither applicable. Furtheremore iI believe you would have to set a coma before and after "together with my belief in my ability". Let's take a step back. We were just saying that you would have to use "have led" if linking work ethic and belief in your ability with "and".
"My work ethic and belief in my ability have led to progress.
This is simply because "and" links 2 noun phrases together as the subject of your sentence. It is both, your work ethic AND your belief, which led to progress. But still it would be more conventional to say:
"my work ethic(,) together with (my) belief in my ability(,) has led to progress."
Now, why is that? Quite simple; "Together" is an adverb.
We did this together. How have we done this? together
Now, iI am equal how not a big fan of "together with" as it seems awkward. but: "together with" is no linker. It is a preposition which normally introduces an adverbial phrase. It does not answer the question who is doing something but rather "how", "through what" or "wherewith/whomwith" something is done. As in "YOU ran a marathon together with 1000 other athlets". Using "together with" in your example would give your work ethics an outstanding role in coomparison to your self-belief, which would only have the sidekick. A perfect example to explain the difference of "together with" and "and" would be the following example:
"the woman passes a man(,) together with some kids"
"the woman passes a man and some kids"
Atleast i would udnerstand these two sentences differently; in the first sentence it is not the man who is together with "some kids" but the women who passes him (though i am unsure about the necessity of a comma). to clarify that the man is standing there with some kids you would have to say;introduce a new clause your adverbial phrase can refer to;
"the woman passes a man, who is together with some kids"
Your believe in your ability becomes a tool rather then an actor should you use "together with". let'sLet's restructure your sentence to illustrate what this means:
"Together with my/the belief in my ability, my work ethic has led to progress"
or more clumsy:
"My work ethic has led to progress, together with my believe in my ability"
Let's have a look at some more examples to clarify what iI mean
He is playing (together) with his friends
He and his friends are playing (alone in their homes)
He and his friends are playing together
I am quite sure the same logic applies to "along with" and "combined with". Nevertheless i doI can't vouch for anything and defenitely not for "as well".