Looks like Arc vs. Clojure has been pretty well covered by the other comments. To take a step back and look at your goals, in case you might find it useful... consider separating the need to eat from your other ambitions.
The demand for hackers is very high right now, so it's easy to find work.
Most people when they get a job and make more money, immediately raise their standard of living. I.e. they find a nicer place to live, they eat more expensive food, maybe buy a car or get a nicer one, etc. But you don't have to do that if you don't want to. You can, if you choose, keep your expenses low while working, and save a lot of money instead.
When your expenses are lower than your income, you don't need to work full time. For example, you could work part time. Or, you could work full time for part of a year and not work the rest of the year.
With "I need to eat" covered, then you have time to pursue your interests without fearing that you're going to starve if you don't get things going quickly enough.
YC has a less than 3% acceptance rate (https://blog.ycombinator.com/yc-portfolio-stats), so applying to YC isn't a great strategy for keeping from starving. (YC is great if what you want to do is build a world changing startup. For meeting your own basic income needs there are many far easier and much more certain ways to do that).
I don't mean to discourage you in any way from applying to YC if you want to do a startup. Just suggesting you have a plan B for the "so I can eat" part :)
I think you might find TripleByte's blog post on what kinds of programmers YC companies want to hire interesting for several reasons:
But keep in mind that for most apps, for most startups, you don't need Lisp. Reddit, for example, started in Lisp and switched to Python because the libraries were better. Nor are most of the YC companies using Lisp.
Of course, every startup is different, and every app is different. For a particular app, or for a particular startup, Lisp might be a strong advantage. For Paul Graham's original startup ViaWeb, for example, Lisp was a decisive advantage.
Lisp is a programmable programming language. When do you need to program your programming language? When your programming language isn't doing enough for you on its own.
As other programming languages have gotten better, there's less of a gap between them and Lisp. ViaWeb was using Lisp competing against companies writing in C++. Nowadays the mainstream languages are higher level.
Lisp is a useful skill to learn because if you ever do get into a situation where it would be helpful to be able to program your programming language you can say "aha! A macro would make this easier!"
And yet, to get into YC, or to write an app that lots of people use/love, most of the time, in most cases, that's not necessary. (Or else startups would be looking for Lisp programmers).