Conducting MaxDiff in a preliminary research project is a great way to think about narrowing the list to focus on the more important aspects in a follow-up CBC.
Our software recommends that each item appear 3x per person in a MaxDiff questionnaire. But, this assumes researchers want and need stable individual-level estimates via HB. If you dig further into our documentation on MaxDiff you will find that we also recommend sparse MaxDiff for aggregate analysis, when the researcher doesn't necessarily need stable individual-level results (e.g., each item might appear just once per respondent). Such can be analyzed using aggregate logit or even low-dimensional Latent Class solutions.
I general, when thinking about aggregate (pooled) analysis, I recommend to people that each item should appear at least 500 times and preferably 1000 times across all respondents and MaxDiff sets.