Ok, all that sounds good.
I will use a very graphic method for explaining my points, it doesn't matter if it looks like a kindergarden method, trust me, it will work fine. :)
A few words about Orchestration....
Colors:
Your instruments are you tools to create sounds, let's compare the instruments with colors:
A: If you place all the colors in the same place, the colors simply get lost, it turns into a combined color, which is not "incorrect" but cannot be used for long, it certainly requires something else.
B: if you place all the color in different place but in a very similar position, they do look different one from the other but still much imagination is expected
C: You can place several colors in the same position for some segments, you create combined colors, but suddenly you move one or two into a different position so it can be noticed by its own, then perhaps can return to be part of a group.
Balance:
Each instrument has its own character in timbre, abilities, and loudness, you will learn to judge the importance of your motifs, harmony elements, melodies, counter melodies, and you'll choose the proper instrument to play each one of those elements of sound.
If a weak instrument is chosen to express something is important for transmitting the idea, it won't work well, same case with powerful instruments playing "decoration" stuff.
D: Powerful lines doing what small should do.
E: Powerful lines keeping the strong structure, small lines keeping "decoration", additional lines to complete the idea.
Now, let's choose your ensemble. I know there's a common rule of using only what you need, although I've seen people using incomplete ensembles, like strings sections with violins and basses only, or flutes and bassoons, well, that could work, but let's just say is far from being recommendable.
The existence of certain instruments in the orchestra has its purpose, and has been defined through many centuries.
I will give you 3 types of ensemble that we can start with:
Minimum:
2 Flutes
2 Oboes
2 Clarinets (in Bb)
2 Bassoons
4 Horns
3 Trumpets (in Bb)
3 Trombones
Tuba
Timpani
Violins I
Violins Ii
Violas
Cellos
Basses
Common: (recommendable)
1 Piccolo
2 Flutes
2 Oboes
English Horn (if no number, we mean 1 instrument only)
2 Clarinets (in Bb)
Bass Clarinet (in Bb)
2 Bassoons
Contrabassoon
4 Horns
3 Trumpets (in Bb)
3 Trombones
Tuba
Timpani
Percussion*
Violins I
Violins II
Violas
Cellos
Basses
Complete Enough (not recommendable to start, but if you feel He-man... )
1 Piccolo (doubling 3rd Flute)
2 Flutes
2 Oboes
English Horn
Clarinet (in Bb) doubling Piccolo Clarinet (In Eb)
Clarinet in Bb
Bass Clarinet (in Bb)
2 Bassoons
Contrabassoon
4 Horns
3 Trumpets (in Bb or C)
3 Trombones
Tuba
Timpani
Percussion*
Harp
Violins I
Violins II
Violas
Cellos
Basses
*Percussion instruments are common more or less in this order:
(unpitched)
Cymbals (Pair Cymbals, aka Clash)
Cymbals (Suspended, may be the very same cymbal used as pair, but you place it in a stand, or other cymbals like "Crash", "Ride", "Splash" others....
Bass Drum
Triangle
Snare Drum
Tam-Tam (this one it is a Gong, just it's correct name is "Tam-Tam" because there are other gongs, we will not use for now)
Toms,
Others....
(pitched)
Xylophone
Glockenspiel
Tubular Bells
Vibraphone
Marimba
Others...
Choose your ensemble and I will speak a little about each instrument, (specify me percussion).
Questions, doubts etc....