> Clarify your goal (...what is the purpose for which you want to build the collection).
> What coins do you want to collect (...am I interested in a specific period, or do I not mind and am looking more for an interesting long-term investment).
> What is your budget (...do I want, and can I, invest funds into the collection as a lump sum or gradually; how much do I want/can I invest in the collection).
> What time horizon do you have for compiling and holding the collection (...am I interested in collecting long-term and want to dedicate myself to it intensively, or do I rather see coins as another one of my many investments and don't have time to follow it in detail).