As the 8-well plate have growth area of 1 cm2, I suggest you should seed your cells around 1x105, the rest of procedure should follow the protocol of lipo3000.
In our lab we use Nest (6, 12, 24 and 96)-well plates and the density of seeded cells is (450k, 160k, 80k and 10k) respectively.
It is worth to mention that those maybe the maximum capacity for ideal seeding, proliferation ...etc. So, you can seed more or less according to your experiment. For example, the mentioned seeding density may not work well for IF, but work well for WB to get enough protein concentration.
Related to transfection, you should seed at a higher density to get a confluency suitable to the suggested ones by the kit of L3K. Of note, I transfected SH-SY5Y cells of a confluency of less 70% with L3K and got an efficiency of ~ 1.7 fold detected by RT-qPCR after 48 h of transfection. However, you have to take in your consideration the localization of your protein, nuclear protein may get less efficiency than cytoplasmic ones (based on a practical experience not on publications).