Hey there, Andy and welcome!
The participants to the group are a very knowledgable bunch.
They have helped me out loads in the past with the odd tip or two.
I hope I can pass on some of their good advice.
All the modifications you list are fairly easy and also as cheap or as
expensive as you want them to be.
For instance, some dealers can charge over a ton for a decent walnut
dashboard, but you can always have a go at making your own from MDF, and
readily available plans. (Google is your friend.)
The only mod which concerns me is the removal of the seat back/rear bulkhead
panel. This may be a structural area though others more knowing may prove
me wrong. The alternative is to put a speaker board under the rear seats
with a decent pair of 6x9s or components sounding adequate for most ears.
Again, plans are available on Google.
Ebay is a good source of spares and the odd donor car or two.
Another good source of tips and stuff is at
www.minifinity.com This is a
free to join web-based mini club who meet up at many, if not all the Mini
events. Well worth a look for dash and speakerboard plans, forums, owners
galleries, events guides and FAQs etc. (Shout out to the boys and girls!)
Buy the HBOL (Haynes Book of Lies), there's loads on ebay.
You WILL swear at the author's lack of common sense, and you WILL hurt your
head on the bonnet catch! (Bonnet quick-release kits cost about a tenner.
Again a shortcut is available. Drill two 3mm holes through the bonnet
hinges BEFORE you undo the nuts. Now when you put the bonnet back on, you
just line up the holes and hey presto! No more banged heads lol )
Don't be tempted by those cheap bullet-type mirrors. I was and they are not
worth the trouble. They sit too low on the door and you can't see through
them. Avoid!
Don't ever, ever mention the modern impersonation of the Mini. It will make
you no friends

(sorry to the regulars but someone had to mention it)
Above all, enjoy the best car ever made! (And don't forget to wave!)
Hope this helps and look forward to your contributions
Karen