Aran Islands

According to the ferry website the shuttle bus departs from Victoria Place in the city center of Galway. Looks like they offer other dropoff points for the return shuttle back into town - to be negotiated with the driver I suppose.
I wouldn't suggest buying your tickets too far ahead. The ferry never sells out and you'll want to check the most recent weather forecast before committing to a particular date and time. The vessels are relatively small craft (about 100 ft in length). Crossings will be cancelled in the event of stormy weather and/or rough sea states, and you wouldn't want to be aboard if conditions are marginal - the boats do rock and roll quite a bit.
An alternative to the ferry is to fly. Doesn't cost that much more and it works a scenic flight into the mix. Plus it avoids the potentially rough crossing by sea. Air Aran Islands

It has been a few years so I hope this info is still accurate. We were given an address by the ferry company and we all lined up on the sidewalk there. Not really a bus station, just a place where the bus stopped and picked up the people for the ferry.

There is also a ferry that leaves directly from Galway, if you are interested in that option. The company is called Aran Island Ferries, and it offers transportation to Inishmore. On the way back to Galway the ferry passes by the Cliffs of Moher. Our family group of nine thoroughly enjoyed this outing last August. I bought tickets about two months before our trip and was glad that I did. Ferry was full... but that was in August. We stayed at the Harbour Hotel right across the ferry dock parking lot - great hotel and very convenient.

The ferry departures from Galway only run seasonally, unfortunately, and according to the Aran Ferries website they cease operation on Sept. 22nd this year.

Looking at the flight to the Aran Islands in a few weeks.

How far in advance to the Aer Arann tickets sell? We have a little flexibility on the day, so would like to make it on a decent day if possible.

I understand there are a couple of small bus tours of the island. Any suggestions? And also how far in advanced do the tours get booked?

For jess: you may want to start a new thread to generate more responses.
You'll need to contact Aer Aran directly, but I'd try to resist any pressure to book too early, ie until you're pretty confident in the weather forecast guaranteeing a nice day.
There will be transportation from the little airport on Inishmore into the town ( or the ferry terminal). There are usually vans and pony traps lined up on the pier to service arriving ferry passengers - it's pretty casual. Just find one you like and hop in. Shouldn't be crowded in April - you'll have plenty of choices,

Thank you! That sounds perfect. We are less than a week out. Weather is looking decent for one of the days, so I think we will take the adventure and go with it!

We flew to Aran Islands (would recommend booking that as soon as you have your dates settled), but the shuttle for both the flight and ferries pick up in front of Victoria Hotel.