you can free up quite a bit of space by creating a USB recovery drive and deleting the recovery data off the tablet. But definitely don't lose that USB recovery drive if you ever need to wipe your Venue to start over.
you cannot easily install metro apps to the memory card. you can do it by moving symbolic links but it's fussy and way over the head of most people. it's why you should get whatever size you can afford. a 32 GB machine will only realistically last a couple years if you regularly get new software. You can ameliorate lack of storage by using cloud storage. But memory cards aren't ideal. e.g., you buy a 32 GB memory card now. then you replace it with a 64 GB down the road which means you're paying for 64 GB but only gaining 32 GB additional space since you have to dump the previous 32 GB card. I have a decent amount of apps and Office 2013. Everything that I could move to the 64 GB memory card was moved. I'm hovering around 3 GB left of free storage. Which means there's not much room for growth in terms of apps.
I have the 32 GB Surface RT and I love it for what it is. I also put in a 64 GB memory card on it which helps a lot (my Music folder was moved there which stores my Xbox Music files as well as my video and documents). I'm not going to regurgitate my thoughts on the Surface RT, but if you're interested, my thoughts are here:
http://forums.windowscentral.com/microsoft-surface-2/279945-too-flakey-relied.html#post2501351
http://forums.windowscentral.com/microsoft-surface-2/279945-too-flakey-relied.html#post2501921
http://forums.windowscentral.com/microsoft-surface-2/279945-too-flakey-relied.html#post2503445
I got mine for dirt cheap during Black Friday for $179 for 32 GB Surface RT with Touch Cover keyboard. I since upgraded it to the Type Cover 2 which is fantastic. The Surface RT has been the best sub $200 computing device I have ever owned.
8" is too small for my needs (my Surface RT is mostly for work). But for reading and web browsing, it's fine. 10.6" is already pushing smallness for me. I love the Surface RT for reading as well.
Great for PDFs (just flick from screen to screen) as well as comic book stuff.
I think you'll like the Dell Venue. I played with it at the store and it was nice. If I was looking for an 8", I'd definitely consider it. Good luck!