no,
you need 2 witnessing to witness your signature, you really are best advised to go to a solictor, there are lots of issues to concern you in a will, not to mind the subject of tax planning
Yes you can. Whether it's advisable to do so or not is a different matter - personally I would go to my solicitor. See here for some information on wills.
Yes you can make your own will. There is a book(s) for sale explaining how it can be done - try Reads / Easons.
However you can also try online (costs circa 17 - 20 euro per will) at http://www.makeyourwill.com/index.htm?aieac*Y000*index for a will.
There was also another irish site [broken link removed] but this has been under re-construction for the last month (or so).
They can pretty much cover a lot of the basics for most people including people who are married and have children.
However if there are complications e.g. you want to create a trust, want to take care of special needs children, want to disinherit someone who would normally be entitled (e.g. estranged spouse), then you need to see a solicitor.
The most important thing is....you need to make a will. Your beneficiaries will thank you especially as they will have to pay a lot less to the solicitor sorting out your estate!
You can do a will yourself but it's not advisable. It's a simple document that is really easy to do incorrectly. For the sake of 100 Euro of so, (ask for quotation on price) it's money well spent getting a solicitor to do it up for you. I would not advice anyone to do a will themselves.