Have a great time Toru!
In your five days, you can easily activate all five GD summits should you wish to.
Lots of information on my website pages - http://tomread.co.uk/gd.htm
Bear in mind that most places on the island stop serving food by 8pm! After that, you can get a curry in Douglas but very little else!
With the current good weather, and the Easter and May Day bank holiday season here in the UK, Snowdon GW/NW-001 will be very busy when you visit - like G3CWI says - in fact it will be very busy even if the weather is bad. 2m FM from a handheld will very likely be the most sensible option therefore from there, but you will make lots of QSOs easily like this.