You call for a strange instrumentation...five clarinets but no bass clarinet? Six flutes but one oboe? Violas I and II, 6 horns? The orchestra's instrumentation isn't extremely flexible, at least not as much as a wind band, and calling for certain unorthodox instrumentations is a guarantee of no performance - especially if you aren't a known composer (I mean stravinsky got away with needing two pianos in some orchestral works, but he's the god damn stravinsky). You can look up standard orchestral instrumentation anywhere, and I suggest you do that. Also, if you divide up a single clarinet staff (or any wind instrument, really) in to multiple instruments, mark it at the beginning as "clarinets 1-2" so whoever is putting the orchestra together knows that's how many you need.
Why does your symphony begin with a full blank measure?
You have this interesting habit of putting dynamics under crescedi/diminuendos. They go in the same horizontal space.
Someone earlier mentioned that octave leaps in the timpani are hard, this is completely untrue. Assuming the notes are on different drums there is no "difficult" interval to play. The difficult thing will be playing the ascending line you have, since it will require changing the pitch of a drum mid-phrase. This is not impossible, a skilled timpanist can change pitch easily. Your range, however, is unplayable. In general timpani parts should be kept between the D below the staff to the A on the top line, but that is a full range of four drums. Occasionally a 20" drum is available that extends the range to middle C, but notes up that high sound thin and ping-y anyway. My suggestion is to do a bit of research into unfamiliar instruments - you can even find some info on wikipedia.
Similarly, your french horn parts are astronomically high. Try not to go above that staff (written pitches) for the most part, and definitely never above written high C.
You notate some rhythms in a very unidiomatic way, as an example I'll correct m. 55 in the timpani part. You have a dotted eighth note followed by a half note followed by a sixteenth rest in a measure of 3/4. In rhythmic notation, it is important to not obscure beats - in a measure of 3/4, the division between all three beats should be clearly seen by the player. This is not to say you have to use three tied quarter notes instead of a half note, but in more complicated rhythms, you should tie over the beats. Specifically, you should notate this with a dotted eighth note, then a sixteenth note tied to a half note, or if you actually want to keep that rest (which is pointless, frankly), a sixteenth tied to a double-dotted quarter, or perhaps to be safe, a quarter tied to a dotted eighth.
I would refrain from tempo markings like "Andante" and instead give a metronome marking...both is fine too, but the important thing is a number.
I have to protest your string parts around m.133 where you notate the same notes but use "8va" and "8vb" over them to change each octave...just notate the different octaves! As a performer, my assumption upon seeing that is that you are too lazy to write different notes and used the "8va" to cut time and effort. May or may not be true, but that's what it seems like.
It looks like over-orchestration isn't a problem for you, which is great, because that is the most common symptom of beginner compositions for large ensembles.
I have literally no idea why you choose to divisi flute 1 and clarinet 2 into three parts while keeping the other flutes and clarinets resting. JUST USE THE OTHER FLUTES AND CLARINETS! Same with horns. You do understand that divisi in wind instruments necessitates additional players, right? Multiphonics being the exception.
I've made it about halfway, but I think I'm gonna stop for now. It's clear you have musical chops, but lack knowledge of instrumentation to truly put together a large-scale work like this. My suggestion is write solos for instruments, and have them played by real players, so you learn by trial and error the things which do and do not work.