1/ You are allowed to travel overseas with 62 kg (140 lbs). You can pay for extra weight but a single suitcase can not weight over 32 kg (70 lbs). That is why I separate the tanks from the rebreather itself.

2/ Concerning the 3 liters tanks.To part the weight of the rebreather I usually put the tanks in a laundry suitcase and never had to open this suitcase eventhough I have some times been choosen to have my bags checked under the X-rays. The tanks are evident on the screen but do not stress the inspector. Of course the valves are loosen so if some one asks me I can show the inside of the tanks. Others have a different experience and had a very hard time to travel with their tanks.

TSA regulations concerning the tanks : http://www.tsa.gov/public/interapp/editorial/editorial_1190.xml ( thanks to Joe Radomski for the info)

3/ Concerning the rebreather itself. I either have the rebreather without the tanks travel in a Samsonite case type OYSTER II 45A*179. In that case, the components are all separated : ABS backplate with straps, counter-lungs, BC, hoses. All the fragile parts of the CCR are inside its black and yellow cover : regs, handsets, pressure gauge. It leaves some room for other little stuff. Another possible suitcase is a large hard model from Carlton, like the airtec 78 cm or equivalent.
I also travel with the rebreather in a big plastic box from Rubbermaid, type roughneck storage box ref 2244 or 2245, with foam at the bottom and the top of the case. This box is very convenient to carry the rebreather around and to keep it protected in boats.
Others use Underwater Kinetics model industrial transit case # 1627 or also a Casefoam model DX 2517-16 or DX 2719-16 .
You can also try the special case with wheels made by Divers Companion.

4/ I believe the scrubber-lid with the cells and the connected handsets and alarm wires should travel in the cabin with you. However nowadays this may only depend on the goodwill of a single TSA or airport officer. So it may be better well packed in a checked-in luggage.