I changed mine last week whilst doing other work, so had the plenum and other bits off already. I would say to take the scuttle off, it takes 2 mins and is much quicker and easier than plenum etc.
Use a flathead screwdriver to prise caps off end of wiper arm fixing. Use 13mm socket undo nut on wiper arm. Spray a little penetrating spray on thread, it will be a little stiff. Ease your wipers off, best to keep threads parallel so comes off easier. I find it easier to do it with bonnet up. Undo fixings on scuttle, torx 25 or 27 IIRC. Move to one side. You should have access to your HBV. I used mole grips because they lock, long nose pliers and normal pliers to get hose clips off. Remember which order pipes connect (take pic on your phone). Tale vacuum pipe off, and coolant pipes. Fit new one. There is no need to drain coolant. But make sure it's not hot when you do it so you don't burn yourself.
I was doing mine as I say whilst doing other work, but individually I'd have thought it'd take no longer than half an hour.
If you can't get a purchase on the clips, I would try lubricating them and gradually moving them round so you can. Either with pliers or rotating HBV, or whichever you can.
In my (limited) experience, most jobs are awkward and fiddly, but straightforward. HTH