Firstly Greetings, great to see new players taking a look after seeing the game at Warhammer Fest. Hope the event was a good one for you.

A1. Approx 25GB in size currently

A2. Currently we have 2 classes to choose from each having 3 starter variants (these variants only denote the starter gear for you) there is only 1 sector open to play with 5 subsystems (2 at level 1 and one for levels 2,3 and 4), each system has a number of planets containing missions to choose from you earn standing for each system for rewards. In addition to regular missions you can do Investigations (small story driven mission sets) or craft yourself Tarots (with fate earnt from regular missions/dailys)for guaranteed rare loot. Party play is working and compatible with all mission types although bugs are to be expected (quite a few have some workarounds) There is also item salvaging/crafting. Level cap for characters is 20 after that you earn account levels for extra points. Daily missions to do and weekly goals to get for rewards. Plus more i have missed no doubt so plenty to do and test/break i've spent 167 ish hours in game thus far and having a blast.

A3. There is little optimisation in game at this early alpha stage but i get decent enough play test results on my rig with an 

AMD FX-6300 with a GTX660ti (2GB) an 8gb Ram  i get between 20-50 fps with med to high settings as long as shadows are off entirely and i'm not doing a 4 player heavy bolter test mission :) . I doubt you will have too many issues as long as shadows and maybe high shaders off too but you have better specs than i it seems so i would at least think it'll run decent enough.

Expect the game to get many overhauls as time goes on wipes/resets etc but mostly have fun testing it if you decide to make the leap of faith.

Happy Hunting Fellow Inquisitors

Playtime kind of depends on what you expect, it looks like the accounts WILL be reset multiple times over the Alpha so if you don't mind that then there is a lot of fun here, I've put in nearly 40 hours since I got it a week ago trying to get new gear, reaching the weekly Glory goals and trying to get my Reputation up in systems. Plus I just like blowing lots of stuff up!

Optimisation is pretty poor at the moment, I have an I7 and a GeForce 570 GTX and this is the first game I can't run on max, in fact I still only get 25-35 fps on medium but you have a newer graphics card so im guessing you can probably make it to high with not many problems. Search youtube if you do have issues, there is a video on there that gives you an idea of things to turn off for FPS gains.

1.) ATM its about 24 GB big

2.) I've played like 14 h in this game. It's in a early state and i dont like grinding if the reward is low (my opinion).  But in co-op it may be more fun (never tried).

3.) I have  an Intel i-5 6600k and AMD R9 380 (4 GB VRAM) and have between 30 and 60 FPS (dependent on how much effects and stuff).