I suggest you wait till you find the need for a second school - so many use points for a second school and find they need to buy them back to get better ones.
From my experience a secondary school is fine but I have ended up dropping it mid mooshu when my power pips can be increased. I do get spells that increase my school spells though such as the blades from Niles and the Sun Spells once I am the level for them.
Altho I have not tried true to your school with all schools I do know it can work with Life, Death and Storm so far though Zafaria.
Use your training points sparingly. Maybe not a full second school, but bits and pieces of others.
Ice to Tower Shield Niles tree in Krokotopia to get Spirit tri-blade and tri-trap Colossus Blvd trainer, train the Reshuffle (always handy!) Fairgrounds trainer (in the Commons), train for shields you may want
If you don't need a second school right now, don't worry about it. Keep your training points handy. Check out the other schools for what you may want. Remember, if you get spells from another school, you will be using MORE pips unless you have a Mastery Amulet for the additional school(s).
Well I am a death wizard, and like many here, I have spent many crowns buying back my training points. Earlier in the game, I would say train ice to tower shield. I started out training fire as secondary, but bought back the points cause I was fizzling too much. After the buyback, I was happy going ice to tower shield. Later on as a death wizard, you will not really find many useful secondary school spells besides the astral schools. I now have about 7 extra training points as of level 65 and only carry one tower shield in my deck. Early in the game the tower shield spell will help you, and you can help others with it too. At a higher level, you will not find much use for a secondary school. Good luck, and welcome to the death school!