1

Many folks travel on the night bus to Flores. I like days myself as I like to see where I am going.. Guatemala is a lovely country. As for the trip to Antigua you can get a shuttle or a taxie right at the airport. You can also arrange with a travel outfit for a private pick up. You can also take a shuttle from Antigua to reach Largo Atitlan. Photos of Guatemala on wolfcalls.com. Yes there may be rain so bring what you need for wet weather.

2

The day or night buses heading to Flores will leave from Guatemala City so you'll have to shuttle there from Antigua 1st. I don't find the scenery especially appealing between GC and Flores so a night bus would work if you think you could sleep (I think I'd have trouble with that so haven't been tempted). That said, Rio Dulce town is mid way on the bus trip so if you go during the day you could stop off there for however long you're interested, either coming or going. Others can pipe in with more current bus info than I have.

Regarding GUA to Antigua, you can just walk out of the airport and choose someone who has "Antigua" on a sign; the cost will be $10 per person. You may have to wait a few minutes for the van to fill and a few minutes on the other end if others are dropped at their hotels/destinations in Antigua before you are.

You can hire a taxi on the spot; cost might be $25-35, depending on your negotiating skills (shared, not per person). When I'm arriving at night I have my hotel - http://www.casa-cristina.com - arrange a shuttle for me, $35 for up to 3; many hotels will make arrangements for you. After a long trip it's kind of nice to exit the airport and see my name on a sign.

Here are 2 agencies I've used for transportation in Guatemala:
http://www.adrenalinatours.com
http://www.rainbowtravelcenter.com

All forms of transit from the airport should accept USD. If you decide you'd rather sleep near the airport and head to Antigua in the morning, here are 2 recommended places that offer free airport shuttles and breakfast in the morning; the 1st is budget, the 2nd midrange, both great value:
http://hostalvillatoscana.com/
http://hoteldoslunas.com/

Happy trails!

3

Regarding, weather, it will be HOT in low-lying areas like Rio Dulce, Flores, and Tikal. The highland areas will be spring-like so I pack a light weight zip-up fleece, even when visiting in July or August. Statistically May is the start of the wet season but generally sees less rain than other months through September. I wouldn't worry about it - no way to predict just what this year will be like.

4

Yes, it is the hottest season. There will be semi-daily downpours just about everywhere but generally they don't last. The Lake is a great place as always to be, as well as some higher elevations like Xela and Huehue which can be very comfortable around now. Lowlands and beach are in basically their hottest month (with April).

5

Take rain gear--last May was extremely wet--Very HEAVY rain almost every day we were in San Pedro.

6

Last year rain started in April here in Antigua, a bit early. Normally we see rain starting in May. A few hours in the afternnon, verly rarely all day long.