Hi! I'm kinda in the same situation as you. I'll be having my ROM on a different day from my banquet. We haven't exactly decided when though, but it should be either a couple of months before the banquet, or the week before (we want a specific date that has a special meaning to us).
1. For us, we're planning to have the ROM on its own, and the tea ceremony will take place on the same day as the banquet. We want to keep things simple, so we'll just have a tea ceremony at the hotel's bridal suite a couple of hours before the banquet on our AD. I'd imagine that gate crashing will take place on the same day as the banquet. As for Guo Da Li, both sides are not very traditional so I think we'll be skipping that.
2. It depends on your personal preference and budget. For us, since our ROM and banquet will be quite close, we'll be keeping the ROM simple since we want to allocate most of our budget to the actual banquet. Possibly, just the closest people will be there (20 or fewer guests), so we'll just sign and then maybe have a meal together. I'm considering having it in a hotel suite or a private dining room (was considering Cassia at Capella).
The charges really depend on your guest list and location, so you have to think about those. It can go up to $100 a person, or it can be as low as $40 to $50. The most no frills experience would be to sign at the registry itself and then all go somewhere together for a meal. You just need 2 witnesses, so the guest list can be as small as 4 or as many as 80+. Typically, most hotels / restaurants have solemnization packages for a minimum of 30 people and the cost can range from $1k to $4 - 5k.
3. Personally, I managed to negotiate with my bridal studio so they're allowing me to use my trial make up and hair session for my solemnization. I'm also converting my tea dress / kua to a long ROM gown, so I'm settled on those. Photography wise, I'll probably source one of the freelance photographers who are looking to build up their portfolio since we're keeping ROM quite simple. I think Bridal Studios do have packages that cater solely to ROM, but it might be more cost effective to have ROM worked into your actual bridal package so you get is as a perk rather than having to pay extra charges for it. Alternatively, you could just buy a nice dress from Topshop or another nice boutique, do your own make up or get a make up artist for about $80 if you're keeping things simple.
I've also heard of some people using the hotel's food tasting session for their ROM, so that's another nice way to save money.
This is my two cents worth, I'd love to see what others have to say!
And congrats!
), I haven't really factored that into my planning. 
But I guess The Aisle has a really wide collection of ball gowns that they don't feature in magazines / on their website. 