You can claim all expenses that are wholly and exclusively an expense for the business. You can also claim a portion of expenses that relate to both private and business use such as electricity, telephone etc.. Your website development costs may need to be capitalised which means that you claim a portion of the expense each year for tax purposes. If you use your vehicle for business and private use a portion of your Fuel, Insurance, Tax, Servicing and Wear and Tear of the vehicle can be claimed as a business expense.
You have to apply for the ROS Login separately through their online system.
Some Accountants offer a Free Consultation to New Start Ups so it might be worth your while arranging a meeting with one to go through any questions you had and it would not cost you.