The authors of the attached article transduced primary T cells with Lentivirus at a ratio of 20 MOI to each one T cell. Therefore, I think it is a good point to start your transduction experiment with.
You can titrate your lentivirus with p24 ELISA and use a GFP encoding lentivirus to titrate how much volume or titre you have (MOI per cell) in your lentivirus preparation by infecting you primary T cells. Later use the same titre or MOI of lentivirus for your any target gene which you want to deliver in your primary T cells. visually MOI (1-10) should be good to avoid multiple integration of lentivirus in a single cell.
In our experience,infection of human T with MOI 10-20 is very well, almost 75% positive. But I would suggest you test a serial MOI gradient of lentivirus on your T cells because different cell state and lentivirus would result in a big difference in infection and expression efficiency.
Genemedi is good at lentivirus production, please find more information on this website: www.genemedi.net/i/lentivirus-packaging