On TheDibb there are dining reports from British people eating both within and outside of Disney. As you are staying at CBR then probably most of your eating will be in your room or within Disney. Disney transport is fantastic and we never hired a car. We have done other theme parks but just used Uber.
Day 3 is usually the day you hit the wall tiredness wise. We tend to do a water park on that day. The time difference can be very hard. Pushchairs are recommended for children up to 6 years old because you will be doing a lot of walking. You will definitely be heading back to the hotel for an afternoon nap.
You can get a grocery delivery to your room for breakfast stuff etc. Food portions in the US are big, very big, easily shareable. This website isn't really updating anymore but the maps are massively helpful
www.easywdw.com/easy/cheat-sheets/disney-world-cheat-sheets-maps-touring-plans-and-wait-times-4/
We fly into Dublin but do that the day before, then fly out of Dublin the next day and clear customs and immigration at Dublin. The downside is you land at 8pm ish which is 1am UK time but my children were/are older. We have been several times.
A couple of things I would recommend, firstly you can get wristbands with your phone number printed on (don't forget both country codes) which your child can wear and then if they get lost a member of staff can ring you. custom-wrist-bands.com/custom-debossed-wristbands-one-colour Ds2 was 7 when we first went and the child's size was good.
Also we take Laken wide neck flasks in, fill them full with ice from the ice machine then fill up with small amounts of water throughout the day. Ice water is completely free in the parks. Hydration is hugely important as is factor 50 once a day sun cream and top it up. Factor 50 swim tops/outfits too.
Bags wise a messenger bag or rucksack can be taken on every ride, even rock n roller coaster which goes upside down, only Tron will have a locker system I believe. We met Joe and Ashley of SeeYaReelSoon on YouTube in Disney at a meet up. Joe has a turtle rucksack and you see him shove it in the footwell of all rides.
And lastly, make sure your children watch some people in Disney so they can see the crowds but most importantly that they understand Mickey etc are massive human sized characters 
And that the wave at Typhoon Lagoon is enough to knock you off your feet, even waist deep! I am completely jealous. Our plan might be to go back next year, even though my sons are teenagers they completely love Disney and Universal.