IPhone 6 messaging problems?

Okay so my iPhone 6 recently has informed me that my storage is full. Then i noticed that my apps kept crashing and my messaging has been messing up. Sometimes it wouldn't let me see the text message and/or switch the order of the messages that were sent and not let me know when i got a text and its bothering me really bad. I assumed it was just my storage so i went from 3,000 pictures to 2,000 and its STILL messing up. If anyone has experience and knows how i can fix this id really appreciate it

Added (1). iPhone 6 messaging problems please help?

Which should I get? Ipod touch 6 or Iphone 6?

If I do get the Iphone 6 I will not have data. The only reason I want the iphone 6 is for the processor and the touch-id, but I only have enough for the ipod touch 6. If the iphone is better I will just save my money and get it later.

New iTunes 12.3 update has me confused?

It's erased all my legally bought and imported CDs, can I get them back? And why when I try to sync my iPhone does it say it's on a different library when I've only used the one laptop for iTunes? How can I fix that so I can sync music again?

Do money supermarket only recommend safe sites?

IIm looking at buying an iPhone 6s and IIm using money supermarket to do so, however are the websites that they recommend all legit or are they only their off price and I ll have to find out myself if they are safe or not?

My music app on my iphone won't launch?

I have an iPhone 6 s that just bought recently. When I click on the music app, I get a colorful background with the word MUSIC next to the apple sign next to it. I tried to reset my iPhone, but it didn't work. I don't have iCloud enabled or anything. This is extremely weird, as I can't find a similar question on the internet.

HOW TO CHANGE NETWORKS ON IPHONE 6?

I'm planning on buying a second hand iPhone 6 Plus which is locked to a tesco network. My previous phone was on 02 pay as you go, if i brought the phone how would i change it onto 02?
If i put my sim card in the new phone would it change to 02? Is that how it works? Would i need to phone tesco up to change it or is it just easier to buy a pay as you go sim to insert into it?

Are payment methods required in new apple id?

I don't have a visa card or anything like that and i recently bought an iphone 6s and when i open the app store or the itunes I'm asked to create n apple id ( a new apple id ). And i tried to do it but when i get to the part where you have to put your payment methods i just stop. So what do i do?
Also, does an empty visa card work? Cause that's all i have