Firstly, depending on your customer base and your costs, it might be advisable to register for VAT even if you don't meet the threshold whereby you would be obliged to do so.
Secondly, it is not too bad that you have only opened a business account now, so long as you have been keeping records of your business expenses. Going forward, try to keep the payments separate as it will make your accounting easier.
In relation to your rent, you cannot pay yourself rent (you just can't "trade" with yourself). However, you could claim a portion of the rent as a business expense. About €200 per month should be reasonable. A portion of the light and heat expenses can also be claimed as business expenses and reduce your taxable profit.
In respect of your van, it would probably be best if you kept a log of business mileage for each month and then claim that proportion of expenses (total mileage on the van should be recorded at the beginning of each month).
Other costs - well, get yourself and accountant and you can claim their fees. Have you a computer, desk, phone etc for this business? You can claim capital allowances on the assets (write the assets off over 8 years).