Hi BZ amost-
Welcome to the forum.
You have been doing your home work.
Numbers 1 through3 - the answers are "True."
Lauterbrunnen could also replace Interlaken as a convenient central place, basd on times to get to various places by public transport.
By October 15, the higher trails above Wengen for example, are iffy, due to possible/probable snow. On the other hand, if the weather is clear, and it can be a that time of year, being in Wengen or Grindelwald can give you fast access to the reallly good scenery. Interlaken , in my biased opinion, is not worth much time.
Four and Five-
The forum has some help -
I personally use a Half fare Card routinely, for multiple trips per year using both rental car and public transport. ( I get the three year version available only if you have a Swiss Address and which costs me about 150 CHF for each YEAR of coverage) but if you spend a lot of time on public transport in a small number of days, one of the Passes, which cover many costs completely, can be a better deal.
I don't understand all the special options...Arno and Annika are the experts.
For number 5, for a brief visit, I'd not bother. If you are inexperienced, maybe even more so. You don't want to keep up with a group. (My opinion.) You can set your own pace. And, you are not in a wilderness. There are a whole lot of trail signs, good maps are readily available at all levels of detail, and once you are there, you will see that it is not easy to get lost.