Depends what your budget is? LOL
Coopers do make some good kits but a change of yeast would make a difference for not that much more cash. That said the Brewferm kits are really good, but more expensive and need ageing to get the best out of them. To be honest a Stout will get better with up to...
If i were you Snail I would try a yeast starter and see what you can get.
I wouldn't use them in a full batch in case (but you might be lucky)
There was an article where someone used 1000 year old yeast from inside a piece of amber.
Tesco's do sales every-so-often like Wilcos, but there kits always seem to be near their sell by dates
I know some people that bought 10+ kits and didn't use them all, be warned
Yep those Oats, you'd have to do a mini-mash to use them in a kit, but no worries. Steep them in a pot and add to your fermenter. I use them with all grain but there is not reason not to use with a kit too.