Congratulations for wanting to put a group together. It can be a lot of work but also very rewarding. My initial thought was...What is the purpose of the group? Is it for lead generation...or for mastermind, education & support? Those are two very different structures and I have been in both. I'm thinking that you are leaning towards the mastermind type of format since you did not have "referrals" on your list and you said "light networking".
Regardless of the format, the policies, procedures, and purpose must be clear and meetings run professionally. The #1 reason guests do not join a group they visited was they felt that the group was too casual, to "cliqueish" and/or the value to them was not evident.
If you already have a core group, poll them for their preferences regarding time of day & day of the week. I guarantee you will NOT get a consensus! You can never find a time that works for all.
The once-a-week exclusive categery model is almost becoming a dinasour as busy people find that schedule too much of a committment. Thus the every-other-week model is gaining popularity. Thursdays is the most popular day for networking events (at least here in San Diego)
The fee would be dependant upon your member base. There is a balance between high enough to "have something at stake", and outpricing them. Is your intent to have this as a revenue-generating business or just covering your costs? I know of one group who uses their fees to hire a consultant to observe their procedures and suggest ways to improve the performance of their leaders and to hire trainers to come in once a month to give one-hour trainings on various business-related topics.
Lastly...Visit every group you can and determine what you like and do not like about them...they all have something you can learn. Then you can structure the type of group that you envision! Good luck... I hope this helps
Mindy