🚀 go-pugleaf

Hi all,

I'm beginning a FUDGE campaign with my preferred, personal mish-mash of a  
magic system.  Beginning mages/wizards/sorcerers must learn spells from  
other mages and cast them in the way that they were taught.  These spells  
are cast in a ritual (words, gestures, and/or components, depending on  
spell).  More experienced magic-users can do without words, gestures or  
components with a penalty, and can affect how exactly the spell works  
(changing the colour of the fire, the range, etc.) with similar penalties.   
(It's just that casting a standard, researched spell is easier.)  Very  
experienced magic-users can design their own spells, trying different  
rituals until they find the one that seems to work best.

Okay, description done with, here come the questions:

Any ideas on how I decide when a low-level magic-user can learn a new  
spell?  when a high-level magic-user can start to design a spell?  how  
complicated a spell they can design?  I can use my judgement a lot for the  
last two, but the first question is tougher; I'd like an objective way of  
deciding that keeps the magic-user at a reasonable level of power.