If you want to fly yourself, then do it. A US PPL will cost a minimum of about $5,000. Add another $1000 or two for not doing it in minimum permitted time. An instrument rating will be ~$7,000, plus an couple of thousand for greater than minimum time. There are plenty of instructors to be found who could fly with you post-licence if you're not confident of your skills. It won't take too long before you'll feel comfortable on your own.
Learn in whatever is simplest & cheapest. You don't need all the bells & whistles while learning the fundamentals of how to fly, nor do you need a 6 cylinder high horsepower engine or extra seats. The money saved can then go towards training onto more advance equipment. It's easier to step 'up' to the whiz-bang avionics having learnt on the basics, than it is to have to step 'down' the other way. A glass panel is not necessary for safe instrument flight, although I would recommend a modern moving map GPS like a Garmin 530 GPS/NAV/COM unit with an XM weather datalink (with the right datalink unit you can even have XM entertainment as well)
Cost of maintaining a US licence is cheap. It never expires, unlike UK/JAR/EASA licences. You will have to do a Class 3 medical which lasts from 2 or 3 years depending on your age, and a flight review every two years. Your instrument rating can be kept current just with frequent flying, sufficient to meet the currency requirements *however* at the early stages of your IFR flying, flights with an instructor at least once a year is a good thing. Even more often if you can. You may find that your aeroplane insurance requires recurrency training, which can also be used to meet the IFR recurrency stuff. In some singles & many twins the recurrency training can be done at dedicated simulator schools. Worth the money, IMO, especially if you're inexperienced. I've done it for PA31 Navajos, and Kingair 90s & 200s to either qualify for insurance, or reduce the premium for the owner.
If you really want to fly high with pax then pressurisation is the way to go. Pax generally don't want to sit with masks on. You also have to make sure the O2 bottle has enough for the flight, whereas pressurised aircraft only require enough O2 in case of pressurisation failure to fly to somewhere where flight at non-O2 altitudes is possible.
There are a few piston pressurised singles around but over those mountains & weather? I think you'd be safer in a twin eg C340, C414, Pressurised Baron- but only with regular refresher training in twin flying. Otherwise perhaps a turboprop pressurised single (or even a TP conversion of a piston single. I'm pretty sure I've seen one for P210.) Make sure whatever you get has an approved de/anti icing system.
Of course, the above is to improve your flight schedule reliability. You can equally do that sort of flight in something non-pressurised and even remaining under visual flight rules. Max altitude will be limited to 17,500' due US airspace rules. You'll just have to be prepared to cancel more often.
20,000' or 26,000' isn't really going to make much difference. I fly a C414 in the high teens/low 20s, and a Kingair 200 in the low to mid 20s. Not much difference except for an occasional severe squall line or front with high thunderstorm tops. Either way I'm still going to have to fly around the tops. I just have to do it more frequently if a fair bit lower.
What ever aircraft you get, training & supervision from someone familiar with the type will soon have you able to manage any peculiarities eg extra fuel tanks or whatever. It doesn't take long for things to become routine. Good training, habits & an appropriate checklist tend to look after those sorts of things.