Summon Night 5 is the worst numbered Summon Night. Though it's probably also the shortest with the least dialogue variation and hidden events so it's probably the easiest for a single translator to handle. A general grounding is Summon Night 3 is recommended; the other references are mostly name drops and so background knowledge isn't as necessary.
Probably the biggest issue will be Rexx and Aty's nickname. Their official position is 大校長, literally something like 'Great Principal,' probably something more like 'Head Principal' for the sake of looking less weird. When Folth and Arca learn who their fishing buddy really is, it's tempting to start rendering 先生 as 'Principal' even if it isn't accurate because it flows better. But Rexx and Aty explicitly say 'it's been a long time since anyone called me 先生,' referring to when they were a private tutor turned general children's school teacher in SN3. You'll need a translation that fits all those contexts or the dialogue loses its depth and meaning. Something like Symphonia's 'Professor' for Raine would probably be best, but actually using 'Professor,' I think, would be a misrepresentation. Rexx and Aty were former soldiers and most of their lessons with their student have to do with combat skills (literally, they learn skills from the lessons). 'Instructor' is probably one of the better options, but it doesn't really roll off the tongue and isn't something you would really call a person, I think. There is the option of starting with one translation for 先生 and switching to 'Principal' after the reveal, but that would be a bit of a tonal shift, I think, especially when I think Rexx and Aty ask that Arca and Folth treat them like they did before.
Also, their hacker will need to put together a system for subtitles. Some endings feature audio-only lines.
7th Dragon 2020 is pretty fun, but I think the person who did 7th Dragon was looking at it. Since 2020 is in fact connected to the DS game, I'd hope that they'll team up with them if it comes to that. Also, Neko's name might present a problem. It's actually a nickname derived from her real name, which, I believe, is Neiko. There's a scene near the end of the game where Neko complains she doesn't like fish, to which one of the nurses responds with 'even though you're a cat?' It's really cute but there's no real way to get the point across without the player knowing that neko = cat. You have to keep her name Neko because it sounds like her real name, so just translating Neko as Cat or Kat or Kitty wouldn't work because then the etymology of the nickname is lost.