Its a hard question really, buy the pro 3 or wait till the Pro 4 is released, all down to when you need it...
I'm also a student (studying Geology) and personally I think that the Pro 3 was a good investment as it WILL replace both your tablet and computer, simply due to portability and power.
Due to the Pro series having fairly decent processors PhotoShop and other 'real' applications will be able to be run easily, however I've heard that throttling is an issue on some programmes (I occasionally use Minecraft and the fans spinning like mad!).
Now then about the Pro 4, as you've said there must be a new surface in the pipeline, what I've heard from forums is that it could either be released along with Windows 10 or next year (apparently Intel is releasing more energy efficient processors next year). If you can manage balancing your tablet and laptop I would wait, as you could get better battery life, however as EMitchell said there could be bugs and other teething problems. If you can't wait (like me!) go for the Pro 3, as there will be hardly any bugs and you'll have the luxury of getting the device at a fairly cheap price.
I was also having the same issue of whether to buy the Pro 3 or 4, my old 1st gen. Surface RT packed up in February and I needed a device for uni so I could either wait 'till the Pro 4 was released or get the Pro 3. Personally I think that the Pro 3 is already a good device apart from the ok battery life 6-7hrs (mix of Office, browsing the web (Google scholar, Web Of Knowledge, Youtube, etc.) PDF and the occasional windows store app), so if battery life isn't an issue got for it

Also IF you do get the pro 3 don't attach the pen to the keyboard (as it falls off!!!)
Hope this helps!