When Steve finds Venus tied up and gagged on the floor in the XL5 jail we then see Volvo in the ejection tube.
Now of all the places. Why put an escape root in a prision cell where crimanals would escape out from ?

Huh? The ejection system is... in the ejection room, not the cell!

Maybe but how did Volvo get there when Zodiac had just opened the cell door?

Venus goes in. Volvo attacks Venus, somehow forces her to open the door (handprint, security pass card, whatever), then closes it when he gets out, and legs it down to the ejection room.

An Interesting theory.
But if Volvo is in the Ejection room and Zodiac is in the cell then why does he say "Goodbye Steve Zodiac." If they are in two different rooms, that is if they are in different rooms.

He's basically saying Ha ha, I have beaten you! Just to himself. A little chuckle. He probably would have just THOUGHT it rather than SAID it.

I love the way the rebels operate. There's two of them, a wimp and one we don't see who is apparently the leader. He dies, and the wimp breaks down in tears. The XL5 crew knock him out.

Steve mentions that they are probably heading for trouble on Platonia. NO!!!!!! Really? Gosh, the fact that you are going off to meet and protect someone who someone else has tried FIVE TIMES to assassinate, and you came to this brilliant deduction?

I love the way the king guy acts. I can't remember his name, so I'll just call him Shorty. Anyway, Shorty does not want to have his drink, and so offers it to his best friend and trusted advisor, Volvo, muttering under his breath 'Probably poisoned.'. And still Shorty doesn't understand why Volvo wants him dead?

He is called Bizzan.

What a silly title.

And in the Control room when XL5 was about to take off, for some reason we see that LT 90 and Commander Zero have swapped seats.....Why?

That happened in Planet 46 as well, 90 watched the missile exploding whilst Zero worked 90's desk.

It also happens in A Day in the Life of a Space General but as General 90 outranks Commander Zero then that's reasonable.

Is it S.O.P for a person to just stroll into a cell with a prisoner, hands full of tray, no weapon, no backup, no radio unit turned on so that others can hear if something goes wrong? How about a nice slot in the bottom of the door to slide the meal tray through?
And where did he get the ropes and gag, anyway?
When Bizzan's name was mentioned, you could almost hear it as "Bizzar", which seemed appropriate. He seemed quite dim. Never noticed that poor, wilted, smoking plant.