I got one of those on recommendation from OMers and back up what outdoordude and Jon have said. I've actually taken the rubber foot off mine cos it kept jamming when I was pulling it out of my rucksack, and don't miss it!
If you don't mind weight and want a bigger flask, I can recommend Aladdin Challengers (1l or 1.8l) . We have 3 and they get regular daily and overnight use as 'teapots' at work and home. Still work well. The oldest is 12 years old.
Also, with cheaper stuff, the smaller the flask, the worse the performance IME. And also, IME lids with spouts n fliptops etc have all failed with regular use.
I wouldn't bother with a tarp for most of the time. OK in gentle weather, but an extra faff, more weight, and a issue in the wind.
Personally, I'd get on with it using techniques as described, or if not managing, get a tent with a better porch (Vango do plenty of models to choose from if happy with the weight - often cheap in winter due to next years models coming up). Another option is unhitch the front of the inner tent and push it back a little to create a temporarily larger porch space?
Pole wise, personally I'd go Black Diamond Trails (or Trail Compacts) if you want quality, reliability and ease of adjustment. But there are plenty out there which are fine.
My usual pan is a little small to risk as a pee pot but I have no hangup about using one for that if necessary. There are no logical arguments against not using your pan if it's washed afterwards? But, as CP says - a milk bottle is more useful - a nice watertight lid can help avoid accidents.
I sympathise with the back pain (I have 2 knackered discs). Luckily, most of the time walking helps my problem unless lots of mountain downhill stuff. But, I carry a lighter pack than I used to though not totally ultralight. Lower packweight always helps..
Just shows we are all different Wayne and so are manufacturers. In many brands whilst a Large size shell, 'fits' , I often need an XL to get enough front length and not have the fabric tight across my shoulders and allow the sleeves to be long enough for my arms. But then I find that there would be room in front for me to be 9months pregnant (if it were possible!) - Pretty much the opposite from you by the sound of things.
TBH, you sound like you may be the standard Paramo shape