I had a 5450 so I feel your pain. It really is terrible for anything besides basic computing. I have no idea why your uncle seems to think you are limited to a certain bus speed. Maybe he feels your CPU is slow enough that any videocard with a larger bus would not be pushed to its full potential.
That motherboard seems to have a UEFI bios, this is good since many newer generation videocards require it. Which brings us to your question. The least expensive new card, with 2gb vram, that I'd recommend in the Nvidia 1030. It happens to be a 64 bit card too by coincidence. It is a vast improvement over your HD 5450. It will do fine with esports games at 1920x1080(ie 1080p). These are games like CSGO, Overwatch, Dota 2, LoL. It's not as good at AAA games, like GTA V and Battlefield 1. However, it's not likely your CPU can run those games that great either so it's not as big a negative as it sounds.
If you can afford to spend a bit more, an RX 460 2gb or GTX 1050 would be better. You get more for your money, plus those cards do pack big jump in performance over the 1030.
All these cards are low in power demands, so they should plug right in and run with no issues. As far as cables go, just use the right one. HDMI to HDMI, or DVI to DVI. Don't use adapters if you can avoid it.