One of my friends is planning to go to WDW sometime in the next year. Is it better to go for low crowd levels (4 and under) or moderate crowds (5-7)? I have read that the staffing and FP for low crowds can impact wait times so maybe moderate is the best way to go?
She is asking me for tips and I am feeling pressure to come through 
I have been during both, September and May, and had a great time both times. We did prefer May, which was moderate, due to the weather, F&G and some later nights. As long as they have a plan and do their FPs and ADRs, I think they will be fine either way
I’m going the end of September/ beginning of October. CLs are all pretty low (4 and under, some parks have 1 and 2s). With the reduced staff people have mentioned, does that mean I should still plan on decent lines? TP customized plans don’t have most waits longer than 15-20 min. Should I build in a number of buffers?
When we went at the end of September in 2016, Food and Wine and the Halloween party certainly affect lines and crowds. We had very low crowds on a party day at MK. However, I would say that for the most part, the stand by lines I saw were pretty equivalent comparing early May 2018 and late September 2016. It could be because we planned well and in May 2018, we found a ton of extra FPs so we could avoid a lot of stand by lines. Like I said before, a good plan, FPs and ADRs will make all the difference.
The TP models are starting to take the WDW reduced staffing levels into account when making wait time predictions, so you shouldn’t have to adjust your plans. Also, it is important to note that the models predict wait times, which are then used to determine the CL, and not the other way around.