I was ready to commit to the Railroad as my main group but looked on the wiki and there seems to be far less missions, is this true?.

Minutemen is shorter, in short, you become enemy with the institute like natural reaction to have to attend an board meeting http://i.imgur.com/6uZjBUr.png

Then the institute will attakk the castle and you get an quest to reach the institute trough an cooling tunnel and then hit the reactor once inside the same way you did for RR.

Actually the RR took FOREVER. The reason why it seems short is because you actually do only a few quests for the RR, the rest you have to do are for the Institute, as a double agent for the RR. Basically in the main stretch of the RR MQ path you are told to "do whatever the Institute wants you to do for now", and this takes forever. For a while there I was wondering who exactly I was even working for anymore. Eventually though you'll be put back on the RR path.

One good thing about it I guess is that if you never intend to actually do the Institute MQ, you can do the RR and still do the majority of the quests you would have done if you were working for the Institute.