Regarding your % question, in my family/social background, we have the following golden rules:
* never spend more than 1/3 of your net income on rent/mortgage repayment
* save and/or invest at least 1/3 of your net income every month
* don't borrow money except when buying a house. i.e. you want to buy a car, or a sailing ship, or you want to go on holiday to the States, you save for it and then you pay cash.
* always have an emergency pot worth 3 months of salary or high enough to meet your outgoings for 6 months - whichever is the highest.
That was in France where our income tax is not taken off our gross salary every month - we have to pay for it every tax year. For someone on a low income, count 10% of your annual net income. On a higher income... the bill can be pretty heavy, especially if you own investments in shares and/or real estate. Some years, my father and uncles ended up paying 50% of their total income in tax, which was maddening!
I was unable to live by those rules until I was 25, as I was not earning enough. From the age of 25 onwards, I did as above, and succeeded in saving the equivalent of 1 year's salary in just 6 years (and buying an expensive laptop and an expensive pair of binoculars, and going on foreign holidays and sailing holidays).
I then lost my job and after several months of fruitless jobhunting in France, I moved to the UK, where the jobmarket/housing market/mortgage availibility were all rosy rosy.
The recession hit the UK less than 1 year afterwards. I have managed to remain employed throughout the turmoil, but I'm still earning less than I was earning in France 5 years ago, and I'm spending a lot more on accommodation. My savings pot is also much diminished, due to frequent housemoves (deposits...), course fees, medical fees...
I'm now applying to better paid jobs and if I get the salary I want, I should be able to start saving nearly 1/3 of my salary again.