Questions about Visit Visa to the UK [closed]

I am in the process of making an application to visit the UK as a tourist. I have already filled in the online application and am ready to submit. I will be attending my friend's bachelor party and then his wedding, while visiting a few friends and stopping by at my University in between (I have lived in the UK for around 6 years previously, 3 when I was very young, and 3 more recently for my degree).

I have a few concerns; first and foremost, I'm currently living in my country of birth, Sri Lanka, and my salary here is abysmal, and I can not afford the trip on my own. My Father is going to pay for everything (he can comfortably afford this) including my flight costs and some extra money for traveling and whatnot. My accommodation and living costs will be handled by my friend who I am visiting (I will be staying with him for the duration).

Do I have to show my salary slips? (I've already arranged to get a confirmation of employment and approved leave letters from my employer)

Do I have to show my own bank statements? (I practically have no savings)

What financial documents from my Fathers' end do I have to show?

Do I have to show flight bookings at the time of application? (I will be getting return tickets, however I don't want to purchase them before my visa is confirmed)

Secondly, when I was in the UK for my degree, I had found out that they mistakenly only gave me 2 years of student visa due to an error in my CAS document. This was corrected by my university, and they sent my passport (to some visa giving authority within the UK, it's marked only as 'Sheffield' on the visa sticker) with a letter saying there was a mistake and to correct the issue, and it was corrected (this was all while I was in the UK) and there was a 2nd visa sticker on my passport (it said residence permit, but clearly mentioned that this was for a Tier 4 Student visa).

Do these count as 2 separate visas? Or just the first one with the 2nd one being noted as 'an application to remain in the UK' (there are 2 different questions on the form, one for visas applied for and the other for 'applications for leave to remain')?

Lastly, I've heard that it's very common for visit visas to be rejected on the grounds that the ECO is 'unsure if I will leave the UK' at the end of my visit, I'm very concerned by this, because I don't want to be rejected especially since it's only 1 month till my planned travel, and I wont have time to reapply if my visa gets rejected after the 3 week wait, and I will miss the wedding, rendering my trip pointless.

So what else should I try and include to prove that I will be returning back? I have traveled to the UK in 3 trips in the past 10 years (for my degree, a year each with breaks in between) and have never overstayed.