"I was instructed to use OpenATV/WB for the iptv plugin but maybe it is available on OpenVix too, have to do some research there." - excuse my ignorance whats WB???
When you are instructed to do something - you should question - Why!
An image is usually a personal choice - but they all basically do the same thing - but offer a few different options - personally I am always confused by OpenATV's various buttons that end up with the same choice.
"I haven't come across Octagon before, are they well supported?" - Yes (German company)- irritatingly so in terms of continuous marketing updates - but they continue to add receiver functionality on latest receiver(SF8008).
"Was looking at the ZGemma, they seem to have a decent support." - Yes - have to say great price/performance
"Is 1GB RAM really enough for a little future-proofing?" - if you are into Kodi etc then check out what the receiver actually offers in flash once loaded with the image.
"Vu+" - quality product at a price, 1st to offer some good hardware and features (like FBC tuners) but gone quiet with the likes of Zgemma and their prices (see Andy I can be nice about Vu+!!)