If you queue in manufacture now, workspace is claimed for those projects. So you end up queueing in your head. Also you have to set the number of techs, but why not always max.
In the list of items you can make, you should be able to multliselect, then like in the sell screen you select numbers to produce. Number of techs always max.
Each item has a priority number, and things of equal prio start simult, and things of lower don't claim space yet.
Either the simult projs get equal numbers of techs, or heavier projects get prop more. I'd say the second.
And there could be a quickprofit key, it starts the most lucrative item and makes unlim and puts it on autosell.