The results of my test run:
The mission's difficulty was all right to me. I tested it only once, on Easy, and I had no problem with completing the mission.
The technical part of the mission is, as kara said, pretty good. I'm happy with your way of doing the briefing stages and playing with the change-iff SEXP. I was also satisfied to see that I could not give orders to the Julius.
Complaints and recommendations, listed in no particular order.
- Of course, I recommend you spellcheck your mission, too. MS Word's spellcheck wil catch most of them. Again, as I already said to someone else, use commas before or after the name of an addressed, like in "Cover me, pilots" instead of "Cover me pilots." It's seemingly minor, but I keep pointing out this sort of mistake because MS Word's spellcheck will likely not find this.
- I recommend you merge the two stages of Command Briefings. You currently have two two-liner stages.
- I'd also recommend you lower some subsytems' integrity a little bit, because a ship starting with 30-some percent hull and all subsystems working 100% is not realistic. Some turrets could be destroyed, for example. I didn't check the campaign's outline, but I assume the Julius came under bomber attacks, so it's reasonable to assume that some turrets and subsystems were hit by bombs.
- Here's something more important: I advise you add the rendezvous navbuoys to the Escort List. Without them being on the EL, they're harder to find. If the player finds a nav buoy (say, by getting within 300 meters), you can use the ship-vanish to make it disappear, as you will no longer need that navbuoy (The Julius remains targettable, so the player won't get lost.) Also, it's
beacon, not
becon.
- When the Obliterator gets within the Julius's beam range, the Julius says something like: "The Obliterator is within the beam range of the Julius." Since it is the Julius that says this, I think it would be more realistic for the captain to say: "The Obliterator is within [our] beam range."
As I said, the technical part of it was satisfying, so was playing the mission. Overall, you deserve a thumb up for this, especially considering that you're a beginner FREDder.

I'll take a look at it in FRED and see what else I can comment.
[EDIT]So, here they are:
- You can use the send-message-list SEXP for successive messages. You can spare some time and effort, because they'll need fewer Events. Just don't forget that you give the delays in milliseconds, not seconds.
- It's good that you have so many messages. It gives your mission a decent atmosphere.
- Why does the Obliterator disable the beams on the Julius if they get within a kilometer range to each other? It's unusual, and without any explanation (like through messages), makes no sense. If you remove this, it will become unnecessary to beam-free-all the Julius twice. Also, why do you use the beam-free-all SEXP if you have set the "All ships beam-freed by default" option?
- Bombers only have orders to attack the Julius. Without anything else, they will just keep flying around after destroying the Julius. I recommend you either make them jump out (makes more tactical sense) or make them attack the fighters (more belligerent, they're Shivans after all.)
That's all for the first run.