Hi,
You will need to look through the self-employed section of the HMRC website to get a full understanding of the taxes and financing. They do try to make things easy to understand. They also have a lot of webinars, if you are into that sort of thing.
You can offset part of the cost of your internet and phone service. For software there are rules depending on type, how long you use it for, etc., but I believe it has to be work specific, not just Microsoft office and that kind of thing.
I wouldn't use an accountant for this level of earnings. It's not that hard to figure out the tax stuff, and you will have to do a lot of the work anyway to provide the accountant with what he or she needs to do your taxes anyway.
Travel, eating out, entertainment, etc. are not generally deductible. There might be exceptions to the travel costs if you are solely traveling on client business, but anything equivalent to "commuting" is not allowed. You can deduct a fairly small amount per month at the standard rate to allow for using your home for business, but it depends on how many hours you work in each month, and you can only count hours of work that is charged out, not overhead, marketing, etc.
But have a look at HMRC's self-employment webpages, everybody's circumstances are different and I really only remember what applies to me. There might be particular things applying to you which make a difference.
Good luck!