Two trains per hour from West Ealing are the Paddington to Greenford service, which I have never seen full to bursting, so
there is a good chance of a seat both ways on those trains.

The other two are Heathrow Connect. I haven't taken it but I'd think
that since he's going in the opposite direction from Heathrow staff
(away from the airport in the morning, toward the airport in the
evening) they shouldn't be too overcrowded either.

West Ealing is in zone 3, so he can either get a zone 1-3 travelcard
for £144.80/mo, or just a West Ealing-Paddington season ticket for
£89.90. The travelcard is good anywhere in zone 3, and will be the
ticket he wants if he's changing to the Underground at Paddington.
If he knows he'll be there for a year, an annual season ticket
is cheaper than monthly and includes a Gold Card which provides
discounts on other rail tickets.