Using a preowned Iphone for Wi-Fi device only, problems I might encounter?

Well my brother gave me his older Iphone to use and I only used it to browse the internet, skype and google voice. Only problem I encountered was at first when I tried to DL a app and it asked for "Apple ID Password" in order to DL any apps, well him being my brother he gave it to me and that was that. Anyways I lost the phone and now thinking of buying another one off a person and was wondering what I need to ask or do in order not to run into this problem again and also would it be better not to get a Iphone?

Can i swim with 500 g on my back?

So I just started swimming and I want to listen to music at the same time. I've been wanting to buy the waterproof Lifeproof case for my iphone 5 for a long time but I need the clip too, to attach it to my swimsuit. That together is around 500 g. Will it be too heavy to swim with on my back? I'm very small and skinny 39 kg / 5'3.

Admission chances in MIT, Princeton and Cornell? My profile is below?

I'm from India and currently studying in class 11th and i'm planning to apply in MIT, Princeton and Cornell University next year.
I have developed many apps in iOS for iPhone - giving video of 2 in supplement(calculator and torch)
I have published an article and had given lectures on that article in various places.
I have done charity work since class 8th - teaching orphan children computers, helping them in many activities, organising programs, etc
I have helped my grandmother during illness giving her all kinds of support
I work experience of website developments
I want to pursue computer science and provide education to poor people using online solution
Ntse 1st stage scholar
Nmtc 1st stage scholar and member association
I will also ask for a big amount of scholarship

class 10th - Cgpa 9.6
Class 11th - 90%+

Sat - 2000

If this is not enough what more should I do?

Apps crash after jailbreaking my iphone?

So I just jailbroke my iPhone 3Gs 5.1.1, and I used redsn0w 0.9.15b3 to do it. I had to run in compatibility mode and as an administrator since my laptop run windows 8, but it was jailbroken successfully. However whenever I try to open up Cydia, Safari, or any other app it crashes. I need to know how to fix this.

I don't have Siri on my iPhone?

I have the iPhone 4S when I first got the phone I had Siri with it. But after downloading iOS 7 I don't have it anymore. Is there anyway I can get Siri back on my iPhone? And I have went into settings to see if I could turn her on but I can't she isn't on my phone anymore.

My iPhone stuck on American App Store?

I accidentally switched the App Store on my iPhone to the American version, how do I switch it back to the UK version? I can't download anything, thanks so much.

I don't have Siri on my iPhone? - 1

I have the iPhone 4S when I first got the phone I had Siri with it. But after downloading iOS 7 I don't have it anymore. Is there anyway I can get Siri back on my iPhone?