Buying gold on credit

Q: Someone wants to buy gold but does not have enough funds and decides to give some amount to the seller and book the gold at the price of the day of booking to prevent paying more by the time he gets more funds. In this case, the gold price may go up or down on the day he will actually give the remainig amount and takes the gold. 

Is this a permissible situation or one needs to do the whole deal of paying money and taking gold in the same sitting?

Following one mazhab

Q: I heard somewhere that all schools of thought are permissible to follow in Islam as long as you only follow one. For example, if I choose to follow Hanafi, I have to follow all of their rulings regardless of what the other schools of thought say. I just wanted to confirm if this is true.

Also, if Hanafis permit something that other schools of thought prohibit, would it be okay for me to ignore the others, or should I avoid it as a precaution?

Hurmat-e-musaaharah becoming established through looking at the private part of a woman

Q:

1. What is the private part of a female that by looking at it hurmat can take place?

2. If a woman is wearing full clothes in a picture or in real life and someone unintentionally looks at her chest and lowers his gaze, and her cleavage is slightly shown, like a very small part of her cleavage, just few milimeters. Does this form part of a females body where hurmat can take place? Even if the person has no lust for her?

3. If a person has shaken hands with an old lady and he is 100 percent sure that there was no desire or lust at that time but he is having waswasa. Should he pay attention or disregard this thought?

Purchasing a house through taking a loan on interest

Q: We live in a country, where it is impossible to buy a house on a full amount, it is more expensive than Europe. My husband is religious and wonts take a mortgage. We have been married for 2 decades and wasted lots on rental property, and the headaches that come with it. Buying ones own house is a basic necessity and advised by scholars, elders, alike if possible.

1. Is buying a house in installments permissible in Islam? From a real estate developer?

2. Can one use an installment plan which is jaiz, from a bank such as Al Rajhi bank?