Is there any reason to have normie trees vs fruit trees? Can I just replace them all?
Well, those Bore ACNL vets will know I made a massive fruit orchard in New Leaf. I had like every fruit in the game in a massive row of trees that took up a quarter of the map. There's no real benefit to doing this. For one, chopping wood is a basic game requirement for DIY and more. When you hit fruit trees with an axe the fruit fall. So any time you want to farm wood you'll have fruit fall on the ground, which will force you to put the fruit in your pockets. And you'll have to pick them up anyways because fruit on the ground rots and it will be considered trash. Your village rating will go down. Tedious work. Think long term and just keep regular trees.
That fruit orchard? Well, spoil alert, a lot of it eventually rotted.
I've been eating my Turnips 
The internet told me prices stayed below 200 
You got trolled. Turnips are the key to the mansion, breh.
Expounding. Let's say you have a million bells and you buy a million bells worth of turnips.
Assuming you bought them at a solid price of 80 bells per turnip, that's a lot of turnips. So then your friend is selling for the amount you said: 200.
Multiply a million bells worth of turnips times 200 per turnip when you bought them for 80 a turnip.
And that's at 200. It often goes up to 500-600.
Whoever told you this is either a moron, doesn't know how to game Animal Crossing, or trolled you. There's a reason we post the prices lol