Ideally you should maintain a separate account for your business this way it is easier to keep track of what is company expense and what is personal expense even though at the end of it all it all goes on your personal tax return (this is a big drawback of Sole Proprietors, along with the fact that if your business gets sued, so do you personally - you are protected in a Pte Ltd Company as it has a life of it's own).
Software? Is it you using it on your personal computer or your company using it on your business computer?

It can get sticky if it's something often found on home PC's, business or no business. Course of the software is business/profession oriented then it's a no-brainer, Accounting & Payroll, drafting/designing, database programming all business oriented.