inception - Why was Cobb so afraid to go into limbo, if he had already gone there and knows that he can use his totem to get out?

1.) When Cobb and Saito were in limbo, Cobb realized he was in Limbo because of the spinning totem. But how did Cobb realized he was in limbo, when he and Mal were stuck there?

2.) And in case it was because Cobb did that by spinning the totem there too, then he should have been very confident to get into limbo every time. He should be not scared about anyone dying in the mission, as he can go to limbo and not forget that he is still dreaming.

EDIT: Added point number 3

3.) And Cobb wouldn't have stopped Eames from shooting Saito. (Saito couldn't have survived even the first level of dream since the first level itself was of 1 week duration). He should have been like "oh sh**.. but ok, I'll go to limbo and get him back." Thats more doable than keeping Saito alive for a week on the first level with a bullet wound on his chest. I don't think they could have used any 'hospitals' since the doctors would have been Fisher's projections.

4.) If it is the case that Limbo is infinite and it is difficult to 'find' anyone lost in limbo, Cobb could have trained the entire team to deal with limbo situation. They spent days training how to carry on the mission and spent weeks of 'dream hours' planning it. Considering the time difference between limbo and actual time, they had enough time to practice it.

FROM THE SCRIPT:

COBB: It's not so bad at first, being gods. The problem is knowing that it's not real. It became impossible for me to live like that.

ARIADNE: But not for her?

COBB: She accepted it. At some point...