yes - get a bigger case
the intellijel case is quite pricey - I'd go for a mantis instead (if you can find one - I see deliverys scheduled soonish in some EU/UK shops) - about 1/2 the price and plastic not aluminium case - the case for them is inexpensive and 1/2 decent these days - nb you wont notice the case once it's full and patched!
1 - good choices - I'd go veils over the intellijel quad though - slightly smaller by 2hp - you might find either a dedicated envelope follower or a dedicated lfo a good thing to add to that set of modules - Maths is great, but it's much better when you patch-program it and don't think of it as just a set of simple functional blocks - see the 'maths illustrtrated supplement' (via google)
you'll also want an instrument interface - the sonicsmith ev1 - seems to be the best in lots of ways - apparently the pitch tracking is great for single note runs etc - don't think it can handle chords - but nothing else can either
if you don't need pitch tracking - there are a number of input modules with envelope following and gate extraction - both are things you really want - and if in the future you want to add pitch following there's one in disting - which is supposed to be not bad - and disting is kind of like Maths in that it's a swiss army knife module - can do lots of things but only 1 at a time - can be daunting if you try to use too many different algos too quickly - just pick a few and set them up as favourites
as a guitarist your hands will be used playing the guitar - consider an expression pedal interface so you can get some control with your feet - addac, doepfer and 7dials all make them - 7 dials is DIY though but as a student you may be able to find someone who'll do an hours soldering for you for not much, or will teach you - if of course you can't solder yourself already!
2 - an audio interface... maybe you already have one and this will definitely work for audio - you may find you need attenuation and amplification - or balanced inputs - you may or may not need a i/o module - I'd try veils for amplification and some passive attenuators before a dedicated i/o module - unless you need balance i/o for your existng audio interface (which I doubt as it's a small prosumer one - at least it's got 4 outs - anything less is a waste of time)
3 - hands and ears and time - read manuals and if you don't understand something in them ask questions (& google 1st - someone else probably already asked the same question before) - remember outputs to inputs - a few passive mults and or stackcables will massively help...
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities