I bought my SP3 with the intention of replacing my laptop and have successfully done so with the i5 256Gb model. However, all I use a computer for is school related activities (writing essays, note taking, use of SPSS, a program used for statistical analysis), surfing on the internet, watching movies and listening to music.
Now, I'm pretty sure these things can be done with the i3 model but my thought process was that if I am about to spend money on a device that will replace my laptop and tablet, and I have the extra cash, I will just go with the upgraded version with some extra storage and hence my purchase of the i5 256gb instead of the i3 model. Also the 8gb ram is nice, I'm not sure if I will ever use it to and extend where the i3 would not have been able to do the same but hey, 8gb is 8gb.
To conclude, for school the i5 256gb will be more than enough! For CodeBlocks, VisualStudio and VirtualBox I am not to sure since I am not familiar with those programs but I have no problems with the programs I use for statistical analysis.
I would imagine that the i5 model will be great for your intentions but if you have the extra money to spend and do not mind spending it, go for the i7 model, you can't really go wrong.
To see how I have set up my study desk you can look at my post in a thread called: [PHOTO] album of your surface pro 3 desk set up. Here is the link:
Good luck, this is the difficult part of buying a device and I am glad I'm over it, haha.