Since most words with "wright" seem to be written together, I would suggest you to keep it that way:
Shipwright, playwright, and wheelwright.
Personal thought: the word "spellwright" sounds great and really will mean "a person who creates, builds, and constructs spells". If you mean "a person who invents or works with spells (also makes them)" then maybe spellcrafter will work. Probably even something like "a spellwright/spellcrafter is skilled in spellcrafting".
There is no answer to which is right. You are making up a word, so to a degree you may spell it how you wish. You are basing it on existing (rare) words such as "shipwright" and "wheelwright", so there can be no objection to spelling it the same way, as "spellwright". But if you wish to hyphenate it for clarity, that would be fine.