In general you get what you pay for. Most of the features you seem to be interested in are only available on machines that cost over $10,000.
Routers use round bits, so inside corners will always have a small radius
no one has done a plasma conversion and even if you could, the slow speed of the maslow would mean you would either get a lot of slag on the back or one would have to cut 1/4" or thicker steel. Steel sheets that big weight several hundred pounds, so you need an overhead crane to move them easily.
I do not think anyone has added a laser to a maslow or a knife, you would have to figure it out yourself, should be possible if you are a serious maker.
There is a youtube series about a diy cnc router which looks like it costs about $1200 after recommended upgrades and takes 50 plus hours to make plus having table saw, miter saw and other expensive tools.
there are Chinese 4x4 cnc aluminum frame machines like www.bulkman3d.com sells might appeal to you more, but they have their issues as well, like floppy lead screws, the open builds facebook or regular website has details.
Everything you make will not be perfect. Learn how to specify the tolerances needed to make the things you desire and buy the best machine within your budget and skill level. Making custom birdhouses might only require +/- 1/16
making custom gears might need +/- 1/64"