Also fake and counterfeit chips should be kept separate from fantasy or other collectibles

May I suggest you try to agree who should contribute which sections in advance, else you will no doubt receive 20 contributions for some topics and zero for others.

2 further points:

Some of the 'smaller' groups of collectibles should probably be grouped together else as suggested elsewhere the list will become endless

Even in 350 words, some topics cant be given justice and may even be misleading. Are you allowing webpage addresses to be included for those wanting to learn more? (Im thinking about things like the club fakes page)