Where ever possible I fish Trebles, unless there's a reason not to. I also fish mainly tubes these days from 1/4" to 3"+, precisely so I can vary the hooks if I need to.
For a relatively new apprentice to fly tying, keep things simple. Tubes are a great way to start before moving on to dressed Doubles or Trebles.
Silver Stoats Tail in tubes and doubles is a great fly to learn the basics on, simple Bucktail Wing and Silver body will give you an excellent fly for both Salmon and Sea Trout.
The Willie Gunn in both Gold body and Black body with Gold Rib, I'd learn to cope with that on tubes initially before moving to dressed hooks.
Once you get a grip of those two fly's on tubes it open's up a vast range of flys that can be tied using the same techniques and just varying the colours and maybe the odd bit of material.
Simple Black and Yellow tube is all you need early season.
Before you move onto dressed hooks, perhaps you should realise Black, Yellow and Orange form the basic colours for many very successful Salmon flies, you won't go wrong with those 3 colours.
Once you get a grip of the basics, you can move to more complicated patterns such as the Cascade or " Allys" series of flies, these style of flies are essentially a different profile of fly which can be quite important.
More so than pattern or style are proportion and volume. You really need to understand these two concepts and apply them to your own efforts. A size 8 double say should always big bigger than a size 10 and so on, same with tubes, bigger the tube and the bigger the overall length of the fly. Then, no matter what you tie, be very aware of NOT! using too much material, if you can see the body of the fly showing through the wing/ hackle then thats what you're looking for, better slim and sparse than big n fluffy!.
Lastly a Cascade does look good on a tube, in fact they're easier to tie like that initially any way, you've more space to learn how to do what you need to be doing.!
Lastly watch anything by Davy McPhail on you tube, he's a legendary flee tier and you'll learn so much from his you tube vids.
When I tie up new to me or difficult patterns, I have a you tube vid. behind the vice and copy blindly stage at a time what I'm seeing on the screen. Don't be afraid of watching several vids. from different Tyers before you yourself start, give yourself as much info as you can absorb, it will help you out.
It will be difficult, often frustrating, but the more you can absorb before you start the better and quicker will your efforts reward you.
Best of luck, Pedro.