Based on the description you are giving, the existing submission style for Science (which has titles and which is what the existing Science Advances style points to) fits all these requirements to the degree possible by CSL (e.g., CSL can't do things like drop "Press" or country names if they are supplied, but my understanding of Science's policies is that they aren't too concerned about that).

https://www.zotero.org/styles/science

I do not know if I am correct. I think seemingly Science and Science Advances both require to include all authors, just like:

I. Friso-van den Bos, E. H. Kroesbergen, J. E. H. Van Luit, I. Xenidou-Dervou, L. M. Jonkman, M. Van der Schoot, E. C. D. M. Van Lieshout, Longitudinal development of number line estimation and mathematics performance in primary school children. J. Exp. Child Psychol. 134, 12–29 (2015).

But currently, they are both like this:

I. Friso-van den Bos et al., Longitudinal development of number line estimation and mathematics performance in primary school children. J. Exp. Child Psychol. 134, 12–29 (2015).

Ah, so the issue with the style you are raising is et al. The style is currently set to use et al when there are six or more authors. The guidelines for Science (which Science Advances just copies—they use the same style) say to not use “et al”, but in the example citations, they do in fact use et al for examples with six or more authors.

As far as I know, there has never been a complaint about this from the Science publication office, and at some point et al is certainly necessary (it is not uncommon for articles with 1000s of authors to be cited in Science journals), so my recommendation is to leave the style as it currently is, considering that it follows the examples given by the journal.

(I see that there is an example with a longer list of authors on the Science Advances page, but this still raises the question of where to cut the list of authors. @adam3smith what do you think here?)

No strong feeling either way. I checked a few recent articles to see what ends up in print:

https://doi.org/10.1126/sciadv.aav4020 (Science Advances; doesn't use et al. even for items with over 15 authors)

https://doi.org/10.1126/science.aap8586 (Science; big differences between HTML and PDF versions, both use et al., but PDF is much more aggressive, and doesn't even show titles for most items)

The submission style for Science is very different from their publication style (that’s why the “no titles” version exists).

I do think seemingly all the authors will be listed no matter how many. This is an example:

http://advances.sciencemag.org/content/5/1/eaat2953 Its 24th citation is as follows:

24. B. Pelaz, C. Alexiou, R. A. Alvarez-Puebla, F. Alves, A. M. Andrews, S. Ashraf, L. P. Balogh, L. Ballerini, A. Bestetti, C. Brendel, S. Bosi, M. Carril, W. C. W. Chan, C. Chen, X. Chen, X. Chen, Z. Cheng, D. Cui, J. Du, C. Dullin, A. Escudero, N. Feliu, M. Gao, M. George, Y. Gogotsi, A. Grünweller, Z. Gu, N. J. Halas, N. Hampp, R. K. Hartmann, M. C. Hersam, P. Hunziker, J. Jian, X. Jiang, P. Jungebluth, P. Kadhiresan, K. Kataoka, A. Khademhosseini, J. Kopeček, N. A. Kotov, H. F. Krug, D. S. Lee, C.-M. Lehr, K. W. Leong, X.-J. Liang, M. Ling Lim, L. M. Liz-Marzán, X. Ma, P. Macchiarini, H. Meng, H. Möhwald, P. Mulvaney, A. E. Nel, S. Nie, P. Nordlander, T. Okano, J. Oliveira, T. H. Park, R. M. Penner, M. Prato, V. Puntes, V. M. Rotello, A. Samarakoon, R. E. Schaak, Y. Shen, S. Sjöqvist, A. G. Skirtach, M. G. Soliman, M. M. Stevens, H.-W. Sung, B. Z. Tang, R. Tietze, B. N. Udugama, J. S. VanEpps, T. Weil, P. S. Weiss, I. Willner, Y. Wu, L. Yang, Z. Yue, Q. Zhang, Q. Zhang, X.-E. Zhang, Y. Zhao, X. Zhou, W. J. Parak, Diverse applications of nanomedicine. ACS Nano 11, 2313–2381 (2017).

More than 40 authors are listed.