(I'll be happy to write a tutorial for you providing a step by step solution for any of these. Except #5; you're on your own there.)
1) Item socketing and sockettable items;
-You could do this several ways. You could simply use a combination of item variables and formulas, or you could throw abilities into the mix and link them to status effects. Either way, you'll need to create an event for combining two items that will alter the socketable item based on what's being socketed, and then destroy what's being socketed. You can also reverse this process by recreating an item via variable changes that were made upon socketing the socketable item and then remove those changes from the socketed item.
2) Item affixes (inc prefixes and suffixes) aka Diablo, Path of Exile, Dungeon Siege etc etc
-Same answer as above (Yes!), but even simpler to implement.
3) Multi-Class; and/or
4) Races and Sub Races in addition to Class / Multi-Class etc?
-These are basically two parts of the same question, but the answer again is a resounding yes. While you can't select more than one class, as I'm sure you know, you could either create a list of secondary hybrid classes (I think Obsidian did this in Pillars of Eternity 2), or you could get clever and create a way to switch to a new class while in game, retaining benefits and progress from the former as you like. This will require some fancy links and workarounds, but you wouldn't need to write any secondary script to force it to work. ORK's standard features alone could do this.
For races, and sub races, I recommend using Defense Attributes. Just create an attribute for race, and then a second for sub-race and include whatever options you prefer in the list of sub-attributes for each. To define the special abilities and what not, you should look to check against subrace as your first priority since the two attributes aren't actually linked in any way other than what you personally set up. Also, it would probably be best if you set your first Sub-Attribute to 'None' in each case so that you don't end up with a slime combatant, for instance, that also happens to be a member of the human race because that's just wrong.
5) Also, where does new ORK stand with integrations with Dialogue System, Behaviour Designer, Love/Hate and with any 'new' Assets like Quest Machine or maybe Emerald AI etc?
-This one I can't really answer, except to say that they were once, and probably are still supported by ORK. It would be better to check those products' websites/forums for answers, as I believe they're actually responsible for keeping up with that implementation.