Hi @BGC , and welcome to the forum!

First of all, I think the Connected E2 Modular is the best TAG Heuer Connected up to now, because it’s the only Swiss Made (and it was the first Swiss Made smartwatch ever), and because it’s the only Modular (you can swap the digital head for a mechanical head in few seconds and without any tool, and also change lugs, buckles, and straps in few seconds and without any tool)

I try to answer your questions:

1) is this a decent price. I think so but looking for some advice. It’s the 41mm version on a black rubber strap and comes with warranty card, box, papers, charger.
Price is decent in case the watch is in good condition, battery is working fine, and screen has no burn-in issues (it would be helpful to have some pictures of the screen showing different watch faces, to verify if screen is ok)

You should also think that this is the 41mm version, mainly designed for ladies, with much less available straps than for the 45mm. Did you try this 41mm version? I did it when I bought my first E2 Modular, and I went for the 45mm because I found the 41 too small, and I don’t have a huge wrist. About mechanical modules, there is only one available for the 41 (Calibre 5), while there are three available for the 45 (Calibre 5, Calibre 16, and Heuer 02 Tourbillon)

2) How compatible is the watch to Apple products (iPhone X)
I use my E2 Modular 45 wlth an iPhone X, and it perfectly works. Bluetooth connection is even more reliable than with an Android phone (I have another E2 Modular 45 tethered to a Samsung phone, so I can compare both options, and I’m more satisfied with how it works with iPhone)

3) with the software being 4/5 years old, should this be of concern and does it mean the watch has a limited life span?
It’s still receiving same Wear OS updates as E3 and E4. It probably will stop receiving updates some day, but in any case, E1 are still running fine and they are not receiving updates since many months ago.

4) any specific questions you think I should ask the seller?
See my answer to question 1): ask pictures of the screen showing different watch faces in bright mode, to be sure there are no burn-in issues (ghost images from other watch faces in pink colour because some pixels are burnt), and ask the seller if the battery is fine (ask how many hours it last when charged at 100%, with the screen in ‘Always on Display’ mode). It should last at least 15 hours

Cheers!