Bkadri

I'm running GTA IV on the base model 2010 MacBook Pro through Bootcamp.
For an old machine it runs fine. 720p/medium textures/low traffic but I'm sure newer models would get better performance. For what I use the game for, just driving around mostly, nothing too intensive, it's fine. I'll probably be getting a new Mac September time. Maybe look at some gameplay on YouTube to get an idea of how well it would run on your MacBook first? Just make sure you're seeing gameplay of your model of MacBook.
I don't know what your MacBook specs are, but I'm sure it would be playable, just very unlikely to be higher than medium settings. If you want to run on high settings, with loads of action on screen then if you can afford it it would probably be worth buying a dedicated gaming PC. GTA IV is almost 10 years old, so running on low settings does look noticeably bad.
If possible, I would set up bootcamp, buy or borrow a copy of GTA IV and see how it runs before you make a decision on buying a dedicated gaming PC. For what you want it for, your MacBook may run the game just fine and save you a load of money.
And Bootcamp will just run Windows exactly the same as a PC, so modding would work exactly the same way as PC. 
 

GTA IV, is not the best, by a long shot. It looks outdated, it is outdated, it constantly crashes.
But if you really want to... can't stop you.
Bootcamp should be able to make it run, provided your macbook actually has the specs to play it.

Best bet for me is get a custom PC, get GTA V, mod the hell out of that because it doesn't crash and looks half decent.