HI there!
I attended the 2013 Expo and had a good time, so might be able to provide some answers to your questions.
So, let's have a go at them....
1. - From what I observed in 2013, and the info I gathered from other during my pre-Expo research stage, Gold Membership really doesn't make any real difference when it comes to attending the Expo.
I specifically recall at the last Expo that Gold Members were furious that the promised 'early admission' via the Members Only line was a total bust.
Most Members didn't get in any earlier then the general public as the incredibly long lines took ages to get into the Anaheim Convention Center.
I wouldn't bother investing the money in Membership if you are thinking it will give you some sort of advantage at the Expo.
From what I saw and have heard in the past, there is no advantage.
2. - Lines to enter the Anaheim Convention Center are insanely long, and it can take up to an hour or more just to get into the building once the doors open for the day.
I kid you not. It's insane!
Lines just to enter wrap several times around the massive venue and the grounds that surround it.
A literal 'sea of humanity'.
That's not the worst of it though...the lines are often very haphazard and confusing, with very little clarity regarding what line is what.
Consider yourself lucky if you can find the actual end of a line...there is no signage and very mixed results when it comes to getting guidance or information from Expo staff.
Be fore warned - you are on your own to figure out where to line up!
Ask the people in line themselves...not the Expo staff...for more reliable info.
The entrance line situation can be a real nightmare.
Friday morning will see the longest lineup, as many camp out inside the venue overnight ( allowed last year ...maybe this year ) so there are hundreds already in front of those waiting outside the doors to enter.
There are also many people who line up outside in the wee hours of the morning hoping to storm the venue once it opens to try to scoop up all the Limited Edition merchandise to re-sell via eBay.
This is a major goal for many in Friday morning.
If you can avoid Friday morning, try to.
Arrive after 11am and you will likely have a far more enjoyable entry experience, although you may miss this opportunity to attend certain panels depending on the schedule line up that day.
Same for Saturday and Sunday...arrive around 11am and walk in like a boss on those days.
Trying to squeeze through the masses in the early morning is too crazy...for me anyway.
The mayhem of entering often causes people to miss morning panels....so be fore warned!
If you absolutely must see a 10am panel, you will need to line up outside of the Convention Center several hours in advance ( exspecially for the Legends ceremony this year ).
As far as lining up for the other panels, many of the smaller more specialized ones feature the Stage Pass option.
This is like a Fast Pass, but for admission into a panel of your choice.
None of the major panels ( Legends, Live Action, Parks & Resorts, etc..) however have Stage Pass...only the smaller ones.
The main panels you will have to line up for in advance, an hour the absolute minimum.
To get a Stage Pass, you will have to line up in a designated area in advance to pick up your pass ticket.
Getting in line early increases your chances of getting to see what you really want to.
The three main Disney related merchandise shops have huge lines as well.
The Disney Store last Expo consistently had three hour waits, and the Imaginnering shop 'Mickey's of Glendale' was consistently a two to hour and half wait to enter.
If you must visit these ( I do recommend 'MoG' of the three) get in line towards the end of the day..like an hour before the venue closes for the day.
3. - Things not to miss at any given Expo are the Imagineering Pavilion and related panel(s), the Parks & Resorts panel, the Walt Disney Archives exhibit, and the general displays of merchandise and other items on the main Show Floor itself.
Each Expo features different displays and themes, but those options typically always deliver.
I also highly recommend stopping by the Imagineering shop 'Mickey's of Glendale'.
Some cool stuff there if you are a fan...more worth the long wait to enter then the Dream Store or Disney Store.
Many underestimate the Show Floor itself...but this is the place to be to bump into various Disney celebrities and other fans.
Be sure to pay attention to those around you...you just might look up and see Marty Sklar or a famous animator standing next to you!
4. - As far as 'tips' I can offer, here are my suggestions to help make the Expo experience better :
First and foremost - BE REALISTIC.
Except in advance that you WILL NOT see and do everything you may wish to.
The schedule of events often overlaps and many activities you might want to partake in will not be possible.
Go into this already accepting this, and you will not be effected negatively by any possible disappointments.
This is not meant to make it sound like this will be a negative experience.
No, chances are..you WILL have a great time but being open minded and accepting what comes your way is a real advantage when it comes to attending an Expo.
It can be very overwhelming attending one of these so pace yourself, don't get too hung up on what you 'miss', and make the best of it.
Attending a Expo is a lot of fun for the most part, but there have been some real horror stories from people who were not at all prepared and expected different results.
Second - DO YOUR RESEARCH.
I cannot stress how important this is, as it will help you better understand and plan for your visit.
Read not only what is posted on the official D23 website, but more importantly read fan reviews from people who have attended.
There are several thread on this very Forum, and many others elsewhere.
Before I attended my first Expo in 2013, I spent a couple of months in advance reading fan reviews.
I was so thankful I did...as I was able to avoid the pitfalls many 'newbies' fall into and had a far better experience knowing what I was getting myself into as far as chaos, confusion, and crowds.
Other tips -
Regardless of what the D23 website says regarding the rules for attending a Expo, DO bring snacks and bottled beverages into the venue with you!
Don't bring a cooler of course...just bring some healthy snacks that will help you keep your energy level up and your dry mouth refreshed.
Take a tote bag or small backpack with you and 'smuggle' in these essentials - granola bars, trail mix, fruit snacks, chips, crackers, nuts, candy treats, etc.
That was my only regret last time I attended...not bringing my insulated travel mug with some ice water.
I will be brining it THIS time..!
I brought plenty of snacks and was glad I did.
There is food availible but it requires standing in long lines and paying for the privilege.
If you want to grab a meal while at the Expo, walk outside and visit the awesome collection of food trucks that are usually lined up in the Convention Center's forecourt area.
Hope this helps answer your questions.
Let me know if there is anything else you are curious about!
-