Whats the factory size? Should be on the compliance plate.
Legally you can only go 50mm over stock, physically you won't fit much more than that under there anyway.
30 x 9.5 R15 are a good sized tyre, common as dirt and you can get them for reasonable money. Going bigger won't get you much further off road and will change your gearing so you have less power getting to the ground. Couriers aren't exactly over powered at the best of times (I had one for 8 years).
I'd suggest you stick with that tyre size and put the money you save into fuel so you can get more experience. 99% of the time a bit of experience will get you further than the biggest tyres you can fit under the vehicle will.
My 2nd. 'pretend' 4wd is a 2005 Ford Courier 2.5L It came from the factory with 265/70/15. (29.6 high )on Alloy rims . I replaced them with 31.5 x10.5 x15 (31in in height) . No winding up the torsion bars was required although I raised it 30mm without affecting cv angle's
yea i know there not a big 4x4 machine hahaha but was gonna go with mud tyres or high profile all terrains. price of trucks now are ridiculous and i cant afford it with my work. so im gonna make do with what i got. but brother was saying get 31 or 32s idk tbh want something to get a bit of a lift out of it