5 short unrelated questions

Question

1. Seguro = sure "I'm not sure" Estoy no seguro. Can it also mean sure like yes? Seguro puede. "Sure you can"? Does this come from seguir (to follow)?

2. I've learned the word for computer to be computadora. I've also seen it translated as ordenador. Are these two words interchangable? The online translation for laptop (computer) is,
   portátil. Or at least that's what the web translation says. Is this correct, or is a better word for laptop (computer).

3. Descargar=to download. To upload is subir?

4. respuesta y contesta: Do they mean the same thing?

5.Comí dos veces desde que te fuiste. I ate two times since you left. Can you leave out the "te" since fuiste can only mean "you left". I don't think you can, but I can't explain why I think that. Also, can "que" be taken out of the sentence? Que is very confusing to me sometimes. It seems like it appears in places that to my baby Spanish brain it doesn't need to be.

Gracias,
peeps