omg! I hate to be a downer but we've made the Barra disaster- although it was about 25 yrs ago. This is what I remember.
(a) There is (was) an "airport" on Barra's cockleshell beach.
(b) The hills and lowlands are hardly walkable, covered on soaking very soggy sphagnum grass. Only walking is on the road (it's not busy as few people live there).
(c) There is only one road - it goes around the island.
(d) There is (was) a car-ferry, Caladonia-McBrain(?) Oban to Castlereigh, Barra's only village.
(e) If you like sheep, you'll love it.
(f) Buses? You are joking dear yizzy - this place is for sheep and their crofters.
(g) In April it's probably terrible for weather, still under the Icelandic weather-trough. Cold and wet.
On the bright side, the beaches are snow-white because they aren't sand but crushed smooth cockleshell residiue. The water is beautiful, clear turquoise.
On balance, after recovering, we found it a remarkable experience, renting a crofters cottage. But never again!
Hope things have improved after all this time but the best advice I can give is cancel unless you are fit, under-thirty and are taking the car.....but even then it's a toss-up!
So sorry but you need to be warned - the beach-photos may look great taken on a sunny(?) day in the warmth of home but it's not a holiday place really.
If proven wrong, I'll be delighted for you yizzy,
Best Wishes,
SIQ.