There's not enough IOs on the board to support Gigabit Ethernet. You can use a USB 2.0 to Gigabit Ethernet dongle which will be 4 times faster than the onboard Fast Ethernet if you have higher bandwidth needs. It will be about half as fast as native Gigabit Ethernet through an RGMII.
Our board has an integrated PHY for the Fast Ethernet. There is one USB 2.0 port with full bandwidth and 3 more that share bandwidth together. This was one of the major performance bottlenecks of the Raspberry Pi 3 Model B since USB IO would interfere with Ethernet IO.
The other boards are based on HDMI 1.4 which supports 4K 30 FPS and no HDR. This has true 4K 60 FPS with HGL HDR support via HDMI 2.0. It also include media decoders that support up to 4K 60 FPS and HDR where as other the boards are limited to 1080P or 4K 30 FPS.
Power consumption is a major limiting factor when designing small boards. You simply cannot fit more powerful chips unless you cut corners on engineering. The other issue is cost. Higher performance chips will add at least $20 to the bill of materials. By the time that is developed into a board with more DRAM and eMMC, you are looking at around $100 higher asking price. The Hikey 960 and the Firefly RK3399 are great high performance boards but they also cost five times the amount. The price prevents them from achieving critical mass to move the ball forward.
The 99 percentile power consumption is below 1A. Almost all MicroUSB power supplies for cell phones will work. If you buy the cheap stuff that cost three dollars shipped, that will probably not fly since they're really 0.5A despite the 2.5A label.
Yes provided they were made for the Raspberry Pi 3 Model B. The power consumption of this device is lower than the Raspberry Pi 3 Model B so if the power supply works with your Raspberry Pi 3 Model B, you should not have any issues with using it to power this board.