1) Few Core Spells - even fewer than we have now. Like 10 Level 1, 6 level 2, 4 level 3, 2 level 4 and 1 level 5 spells in the Core Book. This could be accomplished by moving certain spells to higher levels. Maybe Magic Missile, since it seems to be deemed powerful, you can shift it to 2nd level. And Summoning magic too. It's not hard, would save you work and keep the book light
2) Online Spell Database - with single Spell cards on pdf. Maybe you could post a couple new spells every month or so on the website.
3) Give precise guidelines to create our own spells. I like, in this world where magic is crazy and difficult to come by, the idea that the WIZ might ask me :
"Hey I can cast level 4 spells! Where can i find one?"
I don't want to answer "Look page 120 of the Core Book and pick"
I like "Well you could do some research" He'd discover an ancient crypt where a dark tome is kept, a grimoire of great powers. In that grimoire, I, the DM, can actually put any spell I can devise
While level 1 spells should be somewhat common (in DCC terms), higher level ones should be VERY RARE. Maybe a player will ask you, the DM, " i want to research a spell that allows me and my friends to fly over that chasm." You take some time, maybe run another little adventure in the meantime, have the player roll some (like... 10) spellchecks to see if he got any corruption in the process, then hand him out the Fly spell you devised for him!