Mac mini 2.53 Ghz 4GB late 2009 350 HD 500 EX HD need help in music software production

Garage band is doing my head in because I want to do so much more with my music but I am really confused around the subject of using this software with my computer. So really do hope someone can help me out:) I have tried to find the information on the net but getting even more confused by the minute so I am hoping someone here could answer a few questions http://discussions.apple.com/images/emoticons/happy.gif

My computer is

Model Name: Mac mini
Model Identifier: Macmini3,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.53 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 3 MB
Memory: 4 GB
Bus Speed: 1.07 GHz
Boot ROM Version: MM31.00AD.B00
SMC Version (system): 1.35f1
Serial Number (system): VM0071Q29G6
Hardware UUID: 7BE3019C-654D-5FFA-9EAC-7DE81554B9C0

Can I use Pro logic 9 ? Is cubase pro tools any better ? which is best with the mac mini ?

I have just a standard midi keyboard and m audio interface and just from using garageband I have had interest from a record label but they want me to up my gain.

So i am starting from scratch and want to buy software first then upgrade my keyboard/ So any suggestions on the best route for me to go down ad in software and also for making psy trance and progressive what midi keyboards are good ones to have ?

Looking at pro logic 9 on ebay going at 200 pounds with 2 days to go so anyone can help in this short amount of time I would be very appreciative ?

S