Hey razvitasca, That Level is evil.
I had about 40 to 50 in both attack and defence, as for Health, I recommend having as much as possible. That is, buy Health until you think you've bought more than enough, then buy a little more. The more Health, the better.
There are some really evil Arrows and delete rays that can really mess you up.
The enemies are really strong too, so defence is probably Your best Upgrade, after Health.
It'll take a wile to get used to the BSOD hacks, so I recommend a good number of lives too.
There's no boss at the end though, so you don't have to worry about that.
Note: I'm not, in any way, saying that you should sitt for hours and hours and hours just grinding out bits, cause that's no fun.
It really Depends on the difficulty mod you have unlocked. I have about 340, so each virus gives me around 450 bits.
Oh, and here's a really quick and easy way to earn bits if you have a decent difficulty unlocked
Do this in the program files Level.
1: activate difficulty mod, and set it to it's highest, or a difficulty you are comfortable With.
2: kill either the first virus, or all the ones before the teleporters.
3: Exit the stage, and do step two over again. You can use either Your knife or Your laser.
If you have a good difficulty mod, this can get you bits quite fast.
And, yup, you guessed it...
Try killing Rusty With a difficulty set to ten or higher, if you haven't already done that.
Really hope this helped.