What rank is it a mobster reaches Soldato?

Soldato would be more of a position than a rank.

https://en.wikipedia.org/wiki/Soldato

Fair enough. What rank up in here would be considered a Soldato?

*It does read an elevation in the chain of command from associate.

If you look at the org charts for the traditional structures it's pretty much:

Picciotto > Soldato > Caporegime > Underboss (> Consigliere off to the side advising the boss) > Boss

It's most commonly used to refer to fully fledged members, so made men and above. If you go by the most common definitions of each of the terms you'd probably use Soldato to describe every made member that doesn't have another specific position within the family (e.g. wasn't a capo). 

Thank you for your time TsuDhoNimh.

soldato would be Made Man rank which is the first rank that is manually done by your crew leader...wise guy is the last rank that u automatically can achieve everything after is considered being official member of your crew so therefore it is the crew leader that decides when and if you should attain those ranks