I've done it 6 times now I think, and covered most of the places in your route, which from what I remember you've chosen a lovely route. So I'm sure weather permitting, you'll have a lovely time. It rained solid for 10 days last year, which killed it a bit for us. ;-(
Your first day might be more of a slog than you anticipate, as the long climb up that burn gets pretty hard going underfoot near the top. But as it's your first day, just remember to take it easy and not rush at it. Enthusiasm and adrenalin often carry people for much longer first 2 days the first couple of times they do the TGOC, and then you can feel very tired day 3-4 which leads to a negative mindset.
Day 4 makes sure you start really early. The road over the Corrieyairack Pass has got progressively worse over the years, but that I mean large rocks which can mess with your feet as you rock and roll over them, no matter the footwear you've got. If by then you've got sore feet and blisters then start early, take it slow and enjoy the rest at Blackburn Bothy.
On day 6, when you get to the Glen Feshie bothy don't camp close to it as it is the last place in the morning to get the rising sun. Pitch about 100 m away nearer the river. I've been there and had boots frozen to the ground when it gets chilly, so a bit of sunshine is more than welcome in the morning. It is also a place where a lot of Scots guys go for some male bonding, and this can mean a bit of a ****** racket late at night.
There's going to be quite a few people pitching at White Bridge I understand this year and there isn't much space for more than 3-4 tents. About 1-2km before it there's a wide open space by the river with lots of nice soft ground to lie on!! There isn't much choice after it before you hit the road.
Day 10 you'll already be warned about not camping at Glas-allt-Shiel. The bothy is a very small and dark place. If you want to camp, look for a spot before the decent down to the loch. However by then you'll have made some good friends so you'll have more choices I'm sure.
Day 11 is a long slog especially when you're getting past Shielin of Mark. Hope your navigation is good as a few degrees error adds a hell of a lot of heather bashing to get back on track. But you'll be glad of that Bacon sarnie by the time you get to Tarfside. I prefer to camp on the football pitch in Tarfside rather than stay in the hostel. Then you are right opposite the Mason's lodge for cheap beer at night and you can nip down the road to the Hostel to have a decent shower all for nothing!
Day 12 ask people for a few short cut tips to reduce the amount of road walking on the way to North Water Bridge campsite. Once you go into the village for a well earned cuppa in the cafe, there's a short cut across the river bridge and though the woods which brings you out further down the road and reduces that long LOOOOONNG slog.
Day 13 I think there's another couple of slight short cuts on this day, but it is still primarily a road walk. The cafe has closed a St Cyrus I understand which is a shame, but there's a pub a short walk down the road, which may still be open.
I'm not sure it will help, but if you visit theoutdoorsstation.co.uk website you'll find a 5 part video, and if you search you'll find the 4 audio series of previous crossings, which involve some of the places you are going through.
I hope the weather is kind to you. It was miserable last year, and the previous year I missed there was only 30 minutes of rain in 2 weeks!! I've had snow, storms, gales and rain and a little sunshine. It really is a lovely part of the world on a good day and 'challenging' on a bad one. Make sure you have plenty of tick protection/removers and watch out for the Midge. They are out in abundance due to the warmer weather. I recommend the Gehwol Foot Cream Extra and Refreshing Balm. Never had a blister since I started using them.
Hope that helps. And don't forget to SLOW DOWN!! Everyone makes the same mistake the first time out of the starting blocks. There's no rush. Say 'hi' to John and Roger for me when you get to Montrose.