Questions on twin operation

Hi!

I have a few questions regarding twin operation.

This is all just lofty dreams for me right now, but I want realistic dreams,
hence the questions...:-)

I am a professional bass player by trade.
My instrument is BIG, meaning no way I can get it in my Arrow...:-(

Which twin has the roomiest cabin space, and th easiest back seats to remove
for transporting a bulky item like this?
It should also have quite a big passenger door to get it in in the first
place.

Any of the smaller light twins that would fit this bill?

Next question: I have understood that cost of ownership on a twin is double
that of a single and then some.
Anyone care to elaborate?

I live in Norway, and we have mountains throughout the country, and icing
most of the year, so I'm dreaming of a twin that will climb me to
comfortable cruising of between FL140 and 210, has oxygen (not pressurised)
and certified for ice.

Is what I'm looking for possible?

I have been browsing the controller.com web site looking at Cessnas, Pipers
and Beech, but don't really know any of the pitfalls.

Seams to me you can find twins all the way down in prices below $100K and up
to anything.

What to look for in older, cheaper planes, apart from the obvious TBO times
and run out engines and props?

Anyone ever flown with a double bass before??

Thanks

Frode