Hi rheinlander,
In answer to your first paragraph,.... "When I first started with Trainz, I knew nothing about it"
How did I learn about it?
That was easy. I read the manual, the Trainz-wiki, every thread on the Forum, checked YouTube for Trainz Tutorials, but of course it is even easier now because Trainz have Video Tutorials. See this link,...
http://online.ts2009.com/mediaWiki/index.php/Tutorial_Videos there are 43 of them at the last count.
Once you have that behind you, you should have enough tools and information to create your own routes and even start modelling.
How quickly? That depends on how fast you can read or watch videos.
But, if you want to create routes that you can enjoy,... then take your time. If you make a mistake, don't give up, fix it or scrap it and do it all again. Some routes have taken me years to build. Of course you get better at it as time rolls on by.
A tip: When you download other peoples routes, look for assets that you haven't seen before, scroll your mouse over them and write down in a notebook the name of the asset. You may want to use that in your route at a later date.
Determine accurate positioning 'as in the real world' ? Well, I'm sad to say that because 'Trainz is not the real world', this gives me an opportunity to position things just where I like. I'm the author of my own route. However I do use Google Earth Pro to highlight current and obsolete train and tram tracks.
In answer to your second paragraph,.... "No, I didn't incorporate other peoples routes to create mine"
In my first reply to your queries, I did previously mention, that I spent most of my life in Sydney. So that gives me some insight into what I wanted to include in my route.
Seeking Permission ? If someone designs and creates a specific model, they have a choice whether to upload that asset to the DLS (Down-load-station) or not. So, if it has NOT been made public on the DLS, then they own it! If I wanted to use that persons asset for my route, it is common decency and courtesy to first 'ask permission' from that author if you could use it. It's always wise to respect their wishes.
If you cannot gain their permission, then It's about time to learn modelling skills and create the asset yourself.
I hope this has clarified a few things for you.
Cheers, Roy