It's a lot of work. I've managed to get data from Tiled into my ROM image, and I'm working on figuring out an architecture for scrolling and displaying a status bar.
Implementing scrolling and a status bar sounds simple but is actually a total pain. You only have two screens of tiles to work with, which can be arranged horizontally or vertically, and anything more complicated than scrolling in a single direction (including status bars) requires adjusting the scrolling registers between scanlines, and making sure that your status bar is in a different part of the tilemap (called "name tables") than your world.
A common way to accomplish this is to lay out your graphics memory so a certain address line turns on and off once every scanline, and then putting a chip (called a "mapper") on the game cartridge which wires that address line to a counter, which drives a CPU interrupt line. Simpler games like Super Mario Bros. don't need this extra chip, but you only get a single status bar + scrolling in one direction only. Games with scrolling in both directions often display graphical glitches on the edge of the screen, like Super Mario Bros. 3 (look at the right edge of the screen).
This is unnecessary on newer consoles, and less painful even on the Sega Master System.