Employed and Self Employed?

I am currently employed full time and as such paid PAYE by my employer. In reality I work reduced hours due to a reduction in work coming into the company and recovery from serious heart surgery. My salary has been significantly reduced but I am on paper still employed full time. In order to prop up my income I took on a couple of projects that I was offered as a sole trader since I have no limited company. I therefore need to complete a self assessment to declare the additional income. I also took on a role in a team that organises and runs a not-for-profit business conference and I also volunteer to run industry user groups which are in my local city about an hour away.

What I have been struggling to clarify is what I can claim as expenses against the private work and therefore offset against my additional income on the self assessment I now need to submit. From what I have read I believe I can claim for:

• Travel/mileage at standard rates for meetings I attend
• Stationary/Office expenses incurred as part of this work (pads, pens, printer ink, paper etc)

Can I claim for any of the following?

• Travel and expenses incurred as part of organising business related conferences and events?
• Travel expenses incurred attending training/business events?
• Hardware, i.e. laptop upgrades?
• Percentage of use of mobile phone?
• Anything else?

I appreciate any thoughts you might have on the above, thanks.