I've been thinking... And I've came up with two possible choices for the club's location.
https://en.wikipedia.org/wiki/Salamanca
https://en.wikipedia.org/wiki/Guadalajara,_Castile-La_Mancha (Because not only Mexico has one)
The first currently doesn't have any team, it had a team in the past (that even managed to play in Spain's top flight) but it ended up disappearing twice (it got refunded once) due to bankrupcy.
However, the city stadium still appears on the database (El Helmántico,with a capacity up to 17.100 people which is way more than decent for Liga Adelante standards) which means that you won't have to bother creating one yourself.
Also there a quite interesting choices for derbies since in Liga Adelante there are teams from the same autonomous community such as Valladolid (which it would be one heck of a derby, since it's Castille and León biggest team), Numancia (team from Soria) and Mirandés (team from Miranda de Ebro, Burgos).
Guadalajara is interesting for different reasons, Guadalara is the only region that has been unable to provide players to BBVA (so any regen from a club based there would make history if you ever get to promote), also while Guadalajara already has a club... it doesn't have that much of a history (its biggest achievement is a couple of seasons in Liga Adelante) so the chance of becoming Guadalajara's biggest team is a nice perk.
You should have to create a stadium for the club, unless that you make it share stadium with the other club in the city (sharing stadiums is not a common practice in Spain... but it would make derbies against Guadalajara CF a bit more heated that way I guess).
As for derbies it would have Guadalajara CF as a local one, and also could have Albacete as a local/regional (Albacete is Castille La Mancha's biggest and most famous team) and CD Toledo (another well known team from Castille La Mancha, although is more frequently seen on lower levels like Segunda B and Tercera than Liga Adelante).
It's just a small rambling of mine, but I hope it can be helpful somehow (feel free to pay it no heed if you wish so though).