What people consider to be viable is whether it is used in the meta or what roles they were 'meant' for. I think this is too narrow minded personally. I like to experiment with champions in roles they are not primarily played with, would you consider a blitzcrank to be more viable top than a Nocturne? or an Alistar? In most cases the average league player will shout obscenities for even suggesting that pick, but after the many times I have played both of these champions top, most times it has been successful.(I have played these champions top successfuly on ranked in gold league)
Ranged abilities are absolutely not necessary top lane, or any lane in fact. People cling to the idea that you have to play how they play in the LCS or how the average player plays, but with good experience in the role and with the champion you can play practically any champion. Of course, there are some exceptions (especially when jungle is concerned although I have played successful Jinx + Ziggs jungle games), some champions just don't have what is necessary for that role or are build solely around 1 role that they are just inefficient anywhere else.
In regards to Nocturne, he definitely has what it takes. People will tell you it isn't possible because they failed when they tried. You may even have a few bad games at first but that doesn't mean it is unviable. Nocturne has a good range of offensive and defensive abilties; his Q is great for engaging and chasing meaning it will be very effective for ganks, a spellshield (his W) is always useful especially 1v1, his E is another great 1v1 ability that can turn the tide of a battle as well as making it easy to score a kill when your jungler ganks, his R is what you would be using to engage once you hit 6, it is often the case that many champions who are the meta for top lane don't have amazing engages so when they are ahead they find it hard to keep their lead and stop the opposition from farming, Nocturnes R is a great solution to this problem.
Saying that a ranged champion has the advantage because they can poke and pressure you away from CS is not a reason to dismiss the viability of a champion. I am sure everyone has played as a melee vs say a Teemo top before. Sure, they poke you but a good top laner will bide their time and wait for an opening or for the jungle to come. Usually if they are focusing on pushing you away, they are also pushing the lane. You can take advantage of this and call the jungler to get an easy gank (in regards to Nocturne his Q and R are great gap closers). A melee champion on a level playing field is almost always stronger than a ranged one up close, with sufficent gap closers and CC (that Nocturne has in the form of his Q,R and E) you can easily win against a ranged champion.
At the end of the day it is more about how comfortable you are with top lane and Nocturne in general. I have been playing for years and I feel like I can play many champions wherever and still be successful just becuase I have the experience with that champion to adapt.
I realise you said you don't have many masteries or runes but I will add my advice incase you decide to stick to Nocturne top in later levels.
Go for offensive priority but make sure you put the essential defensive ones in also, a 21/9 spread would be ideal:
I would go for the traditional Attack damage Marks, Armour Seals, Magic Resist Glyphs and Attack damage Quints:
You can build him like a traditional top laner, high damage but also quite durable. I have created a mock up of what my ideal build would be (of course peoples ideas on the best build varies from person to person):
Nocturnes Top Lane Build