Following online guides, in mangle, I have:
1. Guest vlan download connection mark
2. Office vlan download connection mark
3. Upload connection mark for all vlans
4. After those connection marks, there are the corresponding packet marks.
5. Then more packet marks prioriting browsing, youtube, downloads and p2p for each packet marks in #4.

The question is:
Why split up guest and office connection marks (#1 and #2). Can't I create a single download connection mark for everything and then create guest packet mark and office packet mark based on address list.

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Where I am headed is this: in our office there is a group of pcs that is dedicated to livestreaming. I want to give these pcs higher priority for uploads.

The question is: Do you recommend I create 2 connections marks, (1) a connection mark for livestream pc uploads and (2) another connection mark for all other upload source.

Thank you.

Yes its possible to create 1 connection mark for all connection and then create different packet marks based on destination source address protocol port etc. In fact you can create new packet marks without having connectin marks at all but you have to be careful where using pasthrough and where not also you can select no connection mark instead of creating new connection mark prior to new packet mark. Simpler is better for perfomance but if you want to do routing mark for example along with packet mark, without connection mark you have to be careful to select same properties for example for routing mark and packet mark to match the connection speed set in queues. In case where you use connection marks you make changes mainly to to connection mark rules and routing marks, packet marks follow those properties based on connection marks. To create sticky connections and to purge certain connection in connection tracking table in case of a fail over you need connection marks. So depends how simple you want your configuration at the moment and what you want to do in the future to make those choices like to use connection marks or not. For performance you have to keep it simple. For scalability create rules based on topology of the network.