Waiting for my Apollo... is my build ok?

Hey guys, I'm new to all of this (gaming pc's, Digital Storm, and forums, haha), so I really appreciate your feedback.

I decided to order my first custom pc from DS because they had the best reviews. I have never built or tampered with a PC, so the most I know about any components is what I read in reviews. I ordered the Apollo, Level 3, and didn't really change any components. I called DS before ordering to ask if they recommended upgrading anything specific and the nice lady said that it was more than enough. After ordering, I have been so excited that I can't stop browsing this forum. What I noticed is that most buyers use 2 graphics cards in SLI instead of the one gtx980 4g that I ordered.

1) Do you think my build is sufficient for high settings on 1080p with decent frame rates?

2) How difficult is it to upgrade to another gtx980 in sli in the future (if i did upgrade, do i need to change anything else below)

This is what I ordered:

Chassis Model: Special Deal Hot Seller - Digital Storm Apollo
Processor: Intel Core i7 4790K 4.0 GHz (Codename Devils Canyon) (Unlocked CPU) (Quad Core)
Motherboard: GIGABYTE Z97X-SLI (Intel Z97 Chipset)
System Memory: 16GB DDR3 1600MHz Digital Storm Certified Performance Series (Highly Recommended) (Hand Tested)
Power Supply: 750W Corsair CX750M
Expansion Bay: - No Thanks
Optical Drive: DVD-R/RW/CD-R/RW (DVD Writer 24x / CD-Writer 48x)
Storage Set 1: 1x SSD (120GB Samsung 840 EVO)
Storage Set 2: 1x Storage (1TB Seagate)
Storage Set 3: - No Thanks
RAID Config: - No Thanks
RAID Card: - No Thanks
Internet Access: Wireless PCI-E ASUS PCE-N53 (Dual Band Performance) (Supports 802.11n/g/b)
Graphics Card(s): 1x NVIDIA GeForce GTX 980 4GB (Includes PhysX)
Sound Card: Integrated Motherboard Audio
HPC Processor: - No Thanks
Extreme Cooling: H20: Stage 2: Digital Storm Vortex 120mm Radiator Liquid CPU Cooler (High-Performance Edition)
H20 Tube Color: - Not Applicable, I do not have a FrostChill or Sub-Zero LCS Cooling System Selected
Chassis Fans: Standard Factory Chassis Fans
Internal Lighting: Internal Chassis Lighting System (Blue)
Airflow Control: - No Thanks
Chassis Mods: - No Thanks
Noise Reduction: - No Thanks
LaserMark: - No Thanks
CPU Boost: Stage 1: Overclock CPU 4.0GHz to 4.4GHz
Graphics Boost: - No Thanks, Please do not overclock my video card(s)
Memory Boost: - No Thanks, Please do not overclock my memory
OS Boost: - No Thanks, Please do not tweak the services on the operating system
Display: Asus 24 inch 248 Series (Widescreen) (Black) (2ms Response Time) (LED Backlight)
Windows OS: Microsoft Windows 8.1 (64-Bit Edition)
Recovery Tools: Windows Recovery Toolkit (Bundled with Windows CD)
Virus Protection: FREE: McAfee AntiVirus Plus (1 Year Service Activation Card) (Not Pre-installed) ($35 Value)

Thanks FrankW! I really wish that I posted before I purchased; I would have changed those three things. I'm glad that it's not too difficult to add another gpu if needed (but hopefully it won't be).

Thanks bprat22! I can't wait to try it out.