I'm trying to find an explicit minimal set of generators for principal congruence subgroups of $\mathrm{SL}_{2}(\mathbb{Z})$, $\Gamma(N)$ for $N$ all powers of $2$. I know the question has been asked before as to how to find a minimal set of generators for congruence subgroups of special linear groups in the $n = 2$ case, and it was mentioned that there is an algorithm for computing this using Farey symbols. There is a package for Sage written by Chris Kurth which I would like to download, but it seems that I can't find a working link to it. I guess my main questions are as follows:

1) Can anyone tell me how to get this KFarey package on Sage? (Unfortunately, it's probably impractical for large $N$...)

2) Does anyone have any other practical idea as to how to find a minimal set of generators for each $\Gamma(2^{n})$? In particular, if anyone happened to know the answer even for $\Gamma(4)$, it would be greatly helpful to me in the short term.

3) (In case explicit generators cannot easily be found) does anyone know how to compute the abelianization of each $\Gamma(2^{n})$?

Thanks very much!

Jeff