It sounds like a great idea for your guild and you have already covered marketing the event. Consider setting a time limit on the individual speakers to allow others time.
Ask the possible new members for an intro so you can get to know them too. Your group may want to set up mentors for the new members as it can be difficult to break into some groups. Be sure to let them know new ideas are welcome.
Don't forget local colleges (art departments) and local business chambers to get the event in the spot light.