Abandonware doesn't mean free or free of copyright claims / giving you the right to sell it.

The site in question even makes the legality of it quite clear, when defining abandonware (SITE /definition/).

Abandonware France a fait le choix de se spécialiser dans les vieux jeux PC et Mac et en français lorsque cela est possible.
Cette pratique est illégale et n'est que tolérée actuellement.

Translation:

Abandonware France has chosen to specialize in old PC and Mac games and in French whenever possible.

This practice is illegal and is only tolerated now.

So, you'd be selling software for which you have no rights to, illegally IMHO.

As for using RetroPie - see https://retropie.org.uk/about/legal/.
For any software you wish to include (emulators), check if they have a non-commercial clause (even if they're open source), some of the emulators included in RetroPie have this clause in their license.

EDIT: I've removed, per the forum rules, the link to the site.

give me links to stuff with dos