2005 was a big year for electrical changes on the XC70.
So you could have either the earlier electrical system or the later one.
So if you have the earlier electrical system the instrument cluster did suffer form bad / failing solder joints which throws up loads of random errors, if you have the earlier cluster I believe the dials did not have chrome surrounds on them, were as the later cluster did and was not subject to the same problems.
If you have the later electrical system then water/damp in the CEM was a problem, but to check you need to remove the plastic scuttle panel and then the lid of the box were all the wiring enters to check the top of the CEM for water ingress. If you look under the dash in the drivers foot well you can see the CEM the later one is black plastic with no relays just a fuse box.
I would also suggest you read the cods from all modules to see if error codes are stored as this may give you a clue as to were to start looking.
As you have error from multiple systems I would suggest you look at these 2 possibility's first as it going to be some thing central to the system that has the problem.
As Georgeandkira suggested a good charged battery and working charging system is a must I would also suggest having a voltmeter connected so that when it happens you can see if you are getting a sudden voltage change either up or down , I have a cheap digital voltmeter that just plugs in to the 12V socket on the dash , it just gives you a general idea if things change suddenly.