Is this Pc good for the things I want to do with it?

No. the i3 is relatively weak compared to the i5 2500k and pitiful in comparison to the i7 2600K or the i7 980. The integrated HD 4250? will get creamed by even some older games. You would need to upgrade the CPU as well as the Video Card to be able to have a computer you could cal a gaming computer. Multi-tasking is what the 2600K was designed for. Hyperthreading technology is a key feeature your computer needs to have. While the scenario you described could be handle by a dual core it will be slow compared to the 2600k. Having the web browsers open and playing a flash game or something like that would be child's play even for the i3. If you are rendering, encoding or do some other CPU/GPU intensive task and then go, have a browser open with 5 or 6 tabs open and play a game while it does it's things then the 2600k would most definitely be the way to go.