Fortunately, when I started with DesignCAD - back around 1990, when it came from DesignCAD on two 3.5" discs - there wasn't as much choice as you have now!
Do some research into what's available - free, 'free' or even that strange event where you have to pay for something. Then get one, keep your fingers crossed that your research was deep enough to cover all you want to do, RTFM (Read The Flippin' Manual) and start from there.
My first CAD project - still have a paper copy, done on a dot matrix printer (if it hasn't disintegrated by now

) was designing a low winged rudder/elevator pseudo old timer style slimer model of 36" span and laying the plan out to fit a magazine's full sized freeby pullout plan layout. If I can do it, so can you!
Little bit of irony. Not that long ago, when I still had room in shop for such trivia, I drew up a plan using ancient things like 'paper' and a 'pencil' aided by equally ancient drawing aids like set-squares. It took me far less time than it would have done CAD'ing it.
When you lay a pencil line down, you tend to put it in the right place as moving it is a pain. With CAD, you can move the line, make it wider, narrower or a different colour - all of which you will eventually tend to do and which all take up lots of spare time.
CAD is good - just try and use it to draw plans, not develop into a seperate hobby that takes up more time than building little model airplanes
I once got to play with AutoCAD. After a week, my head hurt and I'd drawn a line... DesignCAD might be almost like a kid's toy to a seasoned pro, but for the traditional style of model aircraft plan I've been building from for a while nose, it does me fine.
Sounds like you can draw a model aircraft plan from scratch, good fun learning how to do it on your computer...
D