The question, the comments, even the first revision of this answer are all focussed on kit. A common problem with photographers. We love to talk about kit. Half of us are chomping at the bit to recommend 15FPS mirrorless systems, battery powered studio strobes, the omnipresent 24-70mm f/2.8, the other half want to tell you how they shot an entire wedding weekend on a dusty smartphone.

But kit isn't your main issue. You are.

A wedding isn't just an event you turn up and snap a few photos of what you see. It's the most expensive party your clients will ever throw. They want lasting and equally lavish proof of their outlay. That means you need to take photos of lots of stuff and people you have no emotional investment in. Shockingly few of those photos are going to organically arrange themselves in front of your lens. This isn't nature or street photography, you have to make these set-piece-shots happen —by force if necessary— within a very limited time.

So first up, you need to know what you need photos of. You might have some ideas but you really can't expect your client to lead here. You need to be able to suggest scenes and posed photos, and family/friend arrangements, and different events during that wedding, as well as knowing-by-heart what happens at that denomination of wedding. Much of this will probably mean being familiar with the venue.

Then you need to be able to order people around. Jovially. They know what your job is so they're pretty compliant but they're also bored, hungry and usually getting tipsy by the time you're talking to them. You need to act fast and decisively, again getting everything you need. This takes confidence and presence. For me, at least, that comes with experience.

You also need to know when to get out the way and let the guests enjoy themselves. It's a balance.

There's also a load business stuff you need to learn. Not just to make a profit, but to avoid bankruptcy... How to charge for post-processing. Insurance. Copyright. How to charge for prints. Boring but important stuff. And you need to be able to communicate these nuances to your client as they may expect copyright or post-processing as part of the day fee. Mistakes here (under-charging or under-insuring or not limiting your personal liability) can mean dire things for long term prospects, even from the first shoot. Especially from the first shoot.

So I'll restate this. Kit isn't the main issue. Even if you had the very best kit money could buy, if you take on a wedding client with no real experience, you will miss something important, your client is going to sue you or at the very least, bomb your online reviews. Either way it's a career ender.

But your kit isn't wedding grade either.

Once you know what you're shooting and how to arrange people, your biggest technical challenge at a wedding is light. Medieval churches and converted barns and crappy British weather and "cosy" candlelit corners all conspire to engulf the guests in shadow and ruin every single last shot with blur or noise. Your kit needs to be able to see in the dark.

A good sensor is where I'd start. You're way behind here. Your DX crop sensor is just 43% the size of an FX sensor (and 25% of a Medium Format). A bigger sensor allows a bigger lens to let in more light. And noise control is a feature that keeps improving but you're already 6 years out of date with lower-end dSLR sensors, and ~10 years behind a pro sensors. Not good enough for natural light indoors.

I'd only use your 50mm f/1.8 lens. The kit lens is too damned slow and 70-200mm range is likely going to be the wrong thing, most of the time. Anything slower than f/2.8 is going to ruin a shot. The prosumer lenses also tend to focus faster and be sharper. And if you have more than one lens, you want more than one body. Changing lenses on a single body is a superb way to miss everything or drop a lens.

A 24-70mm f/2.8 is a popular walk-around for wedding photographer. A decent 85mm or 105mm f/1.8 prime for arranged portraits. This is highly in-demand and expensive kit.

You also need flashes and reflectors. And the experience to deploy them to fix a scene, often with only seconds notice and no time to iterate through a pile of settings like you can at home.

But even if you have the very best kit money can buy, you need to know how to use all of it together, in anger, in the location you're at. All while managing your clients' guests and requirements on the day.

If you don't have good enough equipment, or you don't know how to use that £5,000 rental lens, or something lets you down and you miss that shot, it's coming out of your pocket one way or another. Refunds, legal action, a poor review stopping new clients. It pays to avoid mistakes.

In short, it doesn't sound like you're ready for this.

And that's okay. Every wedding photographer was in your shoes at one point.

Just forget about kit for a moment though. You need to learn. The absolute best way you can learn is by volunteering as a dogsbody for an established professional. You might not get paid but it'll be the most useful internship you'll ever take on. Do a summer of weddings and really push them to teach you. Once that's over, reassess your skills.

And as I started with, this photographer will enjoy nothing more than to talk about the kit they're using. They'll probably even sell you some of the older stuff to get you started.

If you absolutely "need to buy something today", keep your D5100 and buy a good flash. There are plenty of knock-offs with the power of a ~SB700... You'll need a remote for off-body because the 5100 isn't a speedlight commander. But anyway learn about light. Indirect light, filtered light. Coloured light. High-speed light. It's a huge subject and thankfully you can practise away from clients.