It's really tempting to be the kid in the candystore, especially when it feels like you're removing the constraints of extract brewing wrt to speciality grains. I think the single most important thing is to just do a brew that is effectively the same at the hot stage for your first 3 all-grain brews, even if you use different hops and yeasts.
That repetition reduces the stress level (as you've done it before) and it allows you to see how changes in procedure affect efficiency etc. Doesn't have to be a SMaSH, but at the same time I woudn't go above say 10% speciality grains to keep it nice and easy for your enzymes. If you're doing it 3 times, then you want a style that you drink a lot of - standard pale ale territory for most people.
You most important tools are pen and paper. Record everything you do - be a bit anal about it with your initial brews.
As above, planning is important. Whilst Brewsmith is probably the gold standard, there's plenty of free options such as
www.brewersfriend.com website or Brewtarget software.
Assume you're going to get crap efficiency the first time round - if you're not using an automated system like a Grainfather then assume 60%, which will mean adding more grain than would be normal once you're in the swing of things. Once your efficiency is up over 70% then you can consider that you've lost your training wheels. The most important aspect of efficiency is repeatability rather than its absolute amount - different systems give different efficiencies, but below 70% generally suggests something is wrong.
Use antifoam -either "official" brewing versions or a dash of anti-wind medication that contains simet(h)icone.
Have a spare bucket to receive the spent grain.
If you're BIABing, then heat/waterproof gloves are really handy for handling/squeezing the bag of grain.
Bulldog clips are useful for helping to keep the bag under control.
Enjoy it!