I've had the opposite issue, after years of clip-ons rearsets etc, I find sitting upright equally uncomfortable. It's just muscle memory....you'll get used to it
There is no right or wrong type of bike. I have rode and toured with guy's on sports bikes, adventure bikes and out and out touring bikes. It really does come down to what you are comfortable with. If you can afford it a couple of different bikes in the garage is the answer to your different riding styles...
Until I actually got a bike I had never thought about having more than 1 but I'm constantly trying to figure out how I can justify giving up food and have a track bike instead.
It would be nice to have more than 1 bike but it's all about priorities. If you ride a lot all year round then it can make sense, but it's expensive keeping a number of bikes on the road especially newer ones with multiple servicing tax and insurance costs not to mention depreciation. A lot will depend on your style of riding as things like a sports bike handle much better, are more likely to get you into trouble and are obviously more uncomfortable but are such fun. Not much use if you're of a certain age and just want to cruise along. Fortunately (or not) I've only got room in the garage for 1 bike. It's a hard life......
Nope been there and done cruisers and would not go back to one now. Having said that I could be tempted on another 1200 speedmaster if I do get bored with the bikes that I currently have.