1- You don't say when you plan to go. May-June and September-October are good times as long as you avoid the Chinese holidays.
2- Don't bring money. Use your bank card and get local currency from ATMs.
3- Yes, this is a typical 2-week plan.
4- There is no need for a guide but if you like to use guide, it can enhance the experience. It depends on your travel style.

How much it costs is entirely up to you. You can sleep and eat cheaply, or you can sleep and eat expensively. You can shop, or not. However, this may give you a start:

https://www.lonelyplanet.com/china/money-costs

Guilin is super touristy. I would go to Chengdu instead, since you will be flying to Shanghai. You will be pushed for time trying to fit in four places as Beijing can easily take a week and Xi'an deserves two full days at least.

You will be better off with a good guidebook and a phrase book than with a guide. There are number of threads on this board explaining why.

You set the budget and spend accordingly. Everybody has different budgets. Some people are fine with a 60RMB hotel room while others don't mind spending 3000RMB per night.

I spent 18 RMB on the hotel room, but the prostitute that serviced the room cost 60 RMB! Yes, some years ago.

@ jobin: Thanks for sharing your experience -- I'm sure we're all better off for your disclosure.

Whether kidding or not, jobin, that's a pretty offensive post. Many of us ladies here would appreciate it if you would remove it.

kja, great to have you back. Did you go on one of your fascinating trips?

I am a woman, not a lady. Maybe that is why I am not offended. Pretending that prostitutes don't exist, and don't troll for clients at hotels, doesn't make them go away. Jobin made no mention of availing himself of the "amenity".

As usual, thursdaysd makes good points. My apologies, jobin, for reading more into your comment than was warranted.

@ CaliforniaLady: Thanks! I'm just back from a month in Peru, which I found fascinating.