Holborn is also on the Piccadilly Line and is very accessible by bus (Waterloo to Holborn is really quick on the bus).
Depending on where in Holborn he's working, it's easy to walk from the northern mainline stations (Kings Cross/St Pancras/Euston). This, together with Waterloo gives loads of options for commuter belt property but note that season tickets for travel are really expensive. You're looking at thousands for an annual pass from commuter belt, even a 3 zone travel card is about £1k per annum. Most employers do a loan so it comes out as a monthly deduction from the pay packet - not sure spouses would also get the benefit though (haven't at any of my employers).
When I worked in Holborn I lived all over the place over the years (mostly within London) and my commutes were like this:-
Docklands (DLR to Bank then Central Line)
Bow in Eastend (Number 8 bus all the way)
Richmond (Overland to Waterloo then bus)
Surrey Quays (Jubilee Line to Waterloo then bus)
West Hampstead (Jubilee Line to Kings Cross then walk or Piccadilly Line)
Crouch End (overland to Kings Cross then walk or Piccadilly Line)
Clapham South/Balham (northern line to Waterloo then bus)
Clapham Junction(overland to Waterloo then bus)
Most people would count a 45-50 minute commute about average and perfectly acceptable. Anything around half an hour is considered very good and anything up to an hour and a half nothing unusual (each way).
Also worth noting that storage within London is VERY expensive. We just rented a 10x10 space (about the size of a garage) for 6 months and it cost about £1000 in Croydon, it would have been 50% more had we rented it in Wandsworth.
I LOVE London but it took me a good 2 years to get used to it. Do come and visit and get the feel for different areas - do you want urban/funky/buzzy/boho/hippy/relaxed/villagey/family/old fashioned/historic/modern/monied/working class/laid back London and its surrounds have it all but it's all SOOOO different and with a tight budget (if that's what you have) you could easily end up somewhere v.grotty if you don't do your homework. Come back with a shortlist and the Londoners will critique it for you!
Good Luck!