I want to start an online business.
I also work full time at the moment.
If I purchase a new laptop and various new office equipment and software for my new start up business. Can I claim all the expenses within my next tax return? If so what is the maximum I can claim on my start up? Would expenses claimed also cover items/servicrs bought online from other countries?

Salary and Wage income is different from your business income.

Regarding claim of equipment - You will be able to claim all the business related expenses against your business income but some items may need to be depreciated over their useful life rather than claimed all at once. There is a small business immediate write off provision available to 30/06/2018 and you can write off anything less than $20,000 as an immediate expense and I would assume there might be very few things you would buy for your start up business that would cost more than $20,000.

Regarding how much you can spend - There is no limit as such. You can spend as much as you want and as required by the business to get it off the ground.

Regarding expense claim from overseas - There is no problem claiming it as a deduction as long as you have a receipt for the good/service.