What does "fifty by fifty" refer to?
Rashi: It refers to the eastern half of the Chatzer, which was completely clear. 1
The Mishkan took up thirty Amos by ten of the western half of the Chatzer, and twenty Amos on both its sides and behind it (on the west) were clear (Rashi). See also Ba'al ha'Turim.
Why does the Pasuk repeat the fact that the sockets were madde of copper?
Rashi: Previously the Torah taught us that the sockets of the curtains were made of copper; now it is coming to incorporate the sockets of the screen.
What vessels is the Pasuk referring to?
Rashi and Seforno: It is referring to the various tools that were needed in erecting the Mishkan and dismantling it - such as hammers, prgs and pillars, all of which had to be made of copper.
If, as the Pasuk states here, the Chatzer was only five Amos tall, then according to those who maintain that the Mizbe'ach was ten Amos tall, the Kohanim performing an Avodah on the Mizbe'ach, was plainly visible from the outside (which is considered lacking in modesty)?
Zevachim, 59b: In fact, the Chatzer was fifteen Amos tall, 1 and when the Torah writes here five Amos, it is referring to the five Amos that extended beyond the height of the Mizbe'ch.
And what 'pegs' is it coming to include?