Do you need both?

I only use Wilcom, but be very careful how you use it. I trust it 100% to reduce the size of a design. It doesn't change the number of stitches, just the size of the stitches. So if you are decreasing the size the final design looks full and dense, which is nice in some patterns. If you increase the size of the design you will find that the design area doesn't fill well. A small increase is OK, but not a big one. From what I can see, Era does almost the same thing except that is limited to 40,000 stitches, you need a permanent internet connection and in a positive side, it has tools for basic digitizing, which I haven't researched on my version of Wilcom

They both convert formats (sometimes complete sections are omitted when doing this), and both will resize the design. In general, I don't think you need both. One will do. They are both free but you have to deal with the ads. Little price to pay for what you get.

So when converting files in TrueSizer, when the message box pops up that says PES Save Option->PES version->Hoop Size
the version is PESV6.0 and the Hoop Size has options of 100x100
180x130 etc and the option for user defined. I've just been leaving it as is (100x100). Is that correct? I'm pretty sure this is something relatively easy but I am the queen of questioning everything (much to my family's dismay).

The 100 x 100 or 180 x 130 refers to the size of the hoop you plan to use to embroider the design.

100 x 100 is the 4 x 4 inches hoop

180 x 130 is the 5 x 7 inches hoop.

Depending on which one you choose, it may tell you if the design is too big for your hoop.

Wow!! I just love this board!! I have learned more in the two days on here than I have in the month I've been scouring the internet!!
Thank you so much!!