There should be a competitive bidding process and if a product or service is purchased in a manner that could personally benefit any board member, that person should state their interest in the issue, and not vote or use personal influence on the matter, and should not be counted in the quorum for a meeting at which board action is to be taken on the matter. A formal conflict of interest policy should be included in the bylaws. A meeting or a portion of a meeting that is restricted to only elected board members who are serving in a voluntary capacity is typically referred to as an Executive Session. Ex officio members may or may not be granted voting privileges so this should be specified in the by-laws of the organization. The expectations for elected board members and ex officio members should be the same.
Some agencies bring on all the new board members at once.
Others have an ongoing admission policy. Both methods are effective. The advantage of bringing everyone on at the same time is that orientation can be done once and on a larger scale. This also takes less staff and volunteer time. However, you can also individualize the orientation process when you bring people on board one at a time.