You receive the error, because you don't supply EA with information, where it should take 'converted' from. Do that by writing b.converted.
But still, there is a logical error in your query. Lets say you have 100 in total an 50 converted. Now you cogroup them together by total and converted. As the two values are different, they won't be cogrouped in one ...
The Problem is, that you don't provide a name for the derived Dimension, so EA uses it for all, cause all do aplly to *.
Try going into the SAQL and rename 'count' to 'countCandidates'.
Then update the "Field" value in the xmd to countCandidate.
Accordingly do the same for other sums and counts.
Alternatively (if you don't want to go to SAQL) you can go ...
Yes. You don't need a catalogue to track what the user does. The catalogue is simply your pool of content or products to recommend to the user as they browse/interact with your site.
But without a catalogue, you won't be able to make personalized recommendations since you'd have nothing to recommend.