For example, we could make 100,000 pencils and 1 Playstation. Or we could make 0 pencils and 5,000 Playstations. But it may be so that we cannot produce 100,000 pencils as well as 5,000 Playstations. The question then is, how much of each are we going to make?
The examples you are giving are not very good since, given today's means of production and modern know-how, society could easily produce 100,00 pencils and 5,000 Playstations.
This question can only be answered completely if we have the consumer preferences of all consumers who choose with their labour credits or money.
Why couldn't this information be obtained from what consumers actually chose to take under conditions of open access to goods? (So, no need for the bureaucracy and waste of resources involved in issuing everyone with "labour credits" and pricing every individual good.)
If make categories of priority this partially solves the problem, but not completely.
For example, pencils will be placed in category 1 and so 100% of requested pencils will be produced (100,000P). But this means that only 1 Playstation can be made, while maybe the consumer preferences would be optimally met if only 50,000 pencils were made and 2,500 Playstations.
So how do we determine where to stop producing one good and start producing another and on what scale?
As I said, in your example, society could easily produce both 100,000 pencils and 2,500 Playstations. More in fact, if needed. The amount to be produced could be calculated from what people took under conditions of open access over a comparable period in the past.
Having said this, there will be problems where if you choose to do one thing you can't do another, but these will concern land use rather than what movable goods to produce. The solution in these cases will be democratic debate and decision. It certainly wouldn't be a good idea to decide such questions by the amount of labour credits or money people are prepared to pay to favour one use as opposed to another as essentially happens today.