first time build, opinion/suggestions please

mmm... your build is missing prices for many of these. I did a little tinkering, and this is what i came up with (I manually entered 400 for the msi gtx970, but you might find it for cheaper somewhere)

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4590 3.3GHz Quad-Core Processor (€184.90 @ Caseking)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (€34.83 @ Amazon Deutschland)
Motherboard: MSI H81M-E35 V2 Micro ATX LGA1150 Motherboard (€59.04 @ Amazon Deutschland)
Memory: Kingston Fury Black Series 8GB (1 x 8GB) DDR3-1866 Memory (€72.90 @ Amazon Deutschland)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Drive (€74.90 @ Caseking)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (€53.28 @ Amazon Deutschland)
Video Card: MSI GeForce GTX 970 4GB Twin Frozr V Video Card (€400.00)
Case: Antec P100 ATX Mid Tower Case (€69.90 @ Caseking)
Power Supply: EVGA SuperNOVA NEX750B BRONZE 750W 80+ Bronze Certified Semi-Modular ATX Power Supply (€71.57 @ Amazon Deutschland)
Optical Drive: LG GH24NSB0 DVD/CD Writer (€18.29 @ Amazon Deutschland)
Monitor: BenQ GL2250HM 60Hz 21.5" Monitor (€99.00 @ Amazon Deutschland)
Headphones: Sennheiser PC330 Headset (€81.99 @ Amazon Deutschland)
Total: €1220.60
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-01-03 22:17 CET+0100

Everything but the motherboard, and headphones are good.(plus the monitor I have a few suggestions)

-motherboard,
the one you chose only has x1 pci-e slots, you do not want this, it will hurt the performance of your card and it only has 2x ram slots... not something you want to put your money it.

here are a few options
MSI 7850-003R
ASUS B85M-E(I would recommend this one)

-Gaming headsets are not worth your money get a quality pair of headphones and a seperate mic,

Headphones
Audio Technica ATH-M40x
Sennheiser HD 518(I would recommend these)
Sony MDR-XB800

Then for the mic
Zalman ZM-MIC1

having one of those headphones and the MIC will sound much better than whatever headset you buy, regardless of price to be honest.

-The monitor you picked looks good; though the Asus VS248H would be a nice upgrade.

@ingatar I took your suggestions and changed a few that I felt could be better,

CPU- Core i5-4690(207)
CPU Cooler- Hyper 212 evo(35)
Motherboard- ASUS B85M-E(77,49)
Memory- Kingston 2*4gb(you can add another 8gb later[be sure to add same type of ram])(77)
Storage- Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive(53.5)
Video Card- Gigabyte GTX 970(360)
Case-CoolerMaster HAF912(76)
Power supply- Cooler Master 750W(79)
Optical Drive- LG GH24NSB0-AUAR10B(18)
Monitor- BenQ GL2250HM(99)
Headphone-Sennheiser HD 518(93)
Microphone-Zalman ZM-MIC1(63)

Total is about €1238

note: here's a review for the headphones
https://www.youtube.com/watch?v=vBUbdkPdiDw

1) ssd's are technically not necessary. that said every pc build since the core2duo or athlon 64 x2 has been largely bottle necked by it's hard drive. frankly, in normal pc operation, outside of actual gaming every pc build with a hard drive feels pretty much identical to each other no matter how old it is. It's due to the colossal slowness of a hard drive (in comparison to the incredible power of the pc). if you want your pc using experience to reflect the incredible processing power of that core i5, then you'll want a ssd. let me put this another way. I have never heard anyone say "i wish i didn't put an ssd in my system", in fact the normal response is typically "i'll never use a standard hard drive ever again"

2) its performs about as good as the 412, at half the price.

3) no one buys acer monitors (or acer anything really). they're junk. the monitor i selected is a high quality gaming monitor. granted it's a little smaller, but it's also high quality.

4) nope. I was aiming to get you a high quality 500W unit. turned out the 750W psu was the same price and better quality then any 500W unit i was looking at. probably a sale or something, but it's just one of those times something had a lot of value and was available.

the one you chose has only 1 pci-e (x1) slot, the x1 will hurt your performance. the one I showed you has x16 plus extra ram slots/pci-e slots so that you may upgrade in the future if you desire to do so.

I do not personally have experience with the headphones, I do have personal experience with a open vs closed ear headphone, in the case you are worried about others hearing what you're listening too then yeah, get a closed pair; however, if that's not a problem gaming with an open headphone is much more enjoyable.(also open headphones are better for clarity/sound stage in music while closed headphones tend to be more bass heavy) do a little research and read some reviews of the headphones, depending on what you like(bass or clarity etc.) you should be able to choose, all three of those above will sound considerably better than the headset you were looking at, so just choose what's right for you!

I have no experience with the antec p100, but I know from experience that the haf 912 has great airflow, can fit any card you want(good for upgrading in the future) and is easy to install components into. Also due to the fact that it is not very expensive I recommend it frequently. That being said, the antec p100 case may be just as good, but if you get the HAF 912 i can promise you that airflow/upgrading will not be a problem in the future .

the cpu was only a little extra from the one you were looking at, it has about a 10% increase in performance, so it's definitely worth the upgrade

I chose the gigabyte version due to the lower price and considerably consistent and good reviews, I do not know of it's performance/volume first hand, but it seems like it doesn't get too loud(I doubt you'd notice much of a difference between the two) and it overclocks well(https://www.youtube.com/watch?v=OAahjdwfbRw), i'm sure the msi one does as well but it's cheaper.

the 750w power supply will allow for more freedom in upgrading later on(plan for the future!)

I personally feel 24 inch with 1080p strikes the sweet spot, but if you don't care about pixel density as much as I do, the 27 inch would be cool(the bigger the better as some would say )

no problem, I'm glad I could help!