I'm also new to this board- I joined a few days ago. I've found this board site to be one of the better ones when it comes to personal advice from experience in DW.
To help ease your stress levels, here are some tips/answers to your questions:
Regarding being turned away if you don't have a reservation, i'm sad to say that is very true. You'll find most all **Character** meals book up at the 180 days out mark from the day of your arrvial because as you can imagine everyone wants to have a meal with their favorite characters! Those meals are the most popular and if not booked at the 180 day mark you may find it very hard to get into a character meal, but never say never. Aside that, the normal disney resturants meaning non-character meals (still just as great and disney themed) you will find you can usually get into some of those much easier because they come in line AFTER character meals. On our last trip we switched a reservation while in disney from one resturant in MK to another one on main street, the day before and had no issue. So ideally it will depend what resturants you want and that will dictate availability. Even if you are past the 180 day mark and know some character meals you want to bring the kids too, call up disney and try to get a spot reserved.
Regarding transportation- if you are staying at a Disney hotel, you get free transportation to everything Disney by bus while you are there. Outside your hotel there will be 3-4 different bus stops with signs letting you know which bus is going where (each bus has a few different stops, example: Hollywood studios may stop at the theme park of hollywood studios, downtown disney and typhoon lagoon) but don't let that worry you either, the stops are quick and painless. I like the travel system disney has made to be quite honest, its fairly quick and convenient. Each bus for each bus stop at your hotel will arrive every 20 minutes. Each hotel has it's OWN set buses, which helps with over crowding. If you need to get to another hotel for a dinner at one of their resturants, simply hop on one of your busses and head to the closest theme park to the hotel you will be eating at and then catch the bus from that theme park to the hotel with the resturant you are eating at. Its not as stressful as it sounds- disney makes everything enjoyable, even the bus rides. The busses are fairly nice and roomy as well and if it's hot, its a nice way to escape to some AC. Don't forget if your staying in a DW hotel you get free transportation to and from the airport to your hotel!
Again regarding dinner- if you do have some reservations made and are running late, simply try to call the resturant if you are able to and let them know your running late but on the way (some may or may not have a direct line, if you can't call and are running late- don't let it ruin your time, just keep on your path and head there anyway, they most likely will still take you). Disney knows travel time is a factor and ESP with kids involved. We were 40 minutes late to our chef mickey reservation and still got a table because we had a reservation prior regardless of being late. I don't recommend being late but if your a few minutes behind don't let it ruin your day, disney will try its best to get you in, and most likely will if you had a reservation.
Don't let all this planning suck out the fun, it should be exciting and know what to look forward to

The way I plan is this:
1) I look at the park hours of each park on each day of our vacation week (I print them as well)
2) I then look at what parades, shows, and fireworks are on what days/nights of our vacation week (I pick out a certain few that we MUST see, and then see what days these fall on. I also print those out)
3) Then I start looking up places to have a sit down meal, even though I know the majority of them, I still do my research. Ideally I start with the top character meals we would like to get into and then pick our second choices to fill in the rest and back up incase one if booked to maximum all day (which happens alot with character meals if not booked at 180 days mark)
4) I THEN, put our week together by park hours, fireworks and shows. Example: we love Fantasmic at hollywood studios and disney has cut back on how many shows it does a week so during our week it was on thursday and sunday, we therefore chose thursday as our day at Hollywood studios. Then I went through our sit down meal choices and the resturant that was closest to that park or in that park we ate at that day (thursday) which happen to be, moms diner. Its easier to plan your days around the park hours or fireworks you want to catch and then pick and chose what nights you will eat at what resturants according to where you know you will be.
I hope this helps a little!