Welcome to the forum, *Old*!
Good on you for spoiling yourself and the kids this Xmas, you're in for a lot of good times with these three rigs "thumbsup"
There are a lot of great suggestions in this thread.
I have a Bomber, so I'll throw my 2 cents in.
1. A metal motor mount is a great upgrade for any rig straight off the bat, but is a must when running big brushless power. A metal mount adds a lot of rigidity over the stock plastic mount, which is prone to flex when subjected to heat and torque, potentially messing up your pinion/spur gear mesh. It also acts as a sort of heat sink to help draw heat away from the motor.
There are a few options out there (Vanquish/Incision, Hot Racing, Axial), I chose to go with the Axial Machined Motor Mount (AX31156) for my Bomber. The transmission for the Yeti/Bomber is pretty much the same, so this mount can be used on both.
One thing to note is that using this mount can cause the stock slipper plate behind the spur gear to foul on the hole in the spur gear cover where the spur shaft enters the transmission. I never had this issue as I upgraded to the Machined Slipper Plates (AX31164) at the same time, which are machined in such a way that they clear with no issues. The other option is to just enlarge the hole in the cover with a Dremel so that the stock slipper plate clears it.
2. Even though Axial markets the new and larger M4 rod ends that are used on the Bomber as "beefier", they are still VERY weak. I broke about 4 or 5 of them before I decided to change out all of the rod ends to Traxxas M4 Revo rod ends (TX5347). These are MUCH stronger, and I haven't had a single one fail yet since I changed them all out.
These Traxxas rod ends are a little bit shorter that the stock Axial ones though, so you may need to add a few M4 spacers/washers to the upper links to correct your rear diff pinion angle, and also to the steering links to correct the toe in/out of the front wheels.
3. Beef Tubes are a great strength upgrade for any solid axle, and they come in a few varieties. I sent my Bomber cartwheeling down a large hill one time, the front plastic axle housing flexed in the process and bent one of the front universal shafts. Beef Tubes prevent this flex, and also provide a solid mount for C-hub/lockout screws to bite into to prevent stripping the stock plastic holes.
My Bomber is more of a high-speed runner, so I chose to go with the Aluminium U4 Beef Tubes in both front and rear axles. They are super light but add a lot of strength and rigidity. If you're going to be doing more crawling/trailing, you may want to consider the steel or brass Beef Tubes, which add a good bit of weight down low to keep the vehicle planted. Some people run a combination of both, with steel/brass in the front for low weight in the front axle to help with climbs, and aluminium in the rear for strength with no added weight.
All depends on what you plan on doing.
3. You're on the right track with Team KNK stainless hardware.
I would suggest getting a bunch of spare hardware to keep on hand in case you strip/lose some screws. Team KNK do a fair few different varieties to keep you covered. Unfortunately, nobody here in Australia really carries Team KNK stuff, but I ended up finding an eBay seller in Hong Kong that sells stainless fasteners.
I ordered a whole bunch of all different sizes and it is something that you don't quite realize how useful it is to have on hand until you actually have them on hand, haha.
In addition to the hardware, I highly suggesting having a bunch of shims/washers of various sizes on hand as well. These are useful if you need to shim the diff gears to set the mesh (I had to shim my rear pinion shaft between the driveshaft and the outer bearing to keep my pinion pulled away from the ring gear slightly) or place behind the wheel hex pins to eliminate any in/out axle shaft slop (again, I had to place a washer behind each hex pin for this reason). You will need 5mm shims for pinion shafts/gears and for the axle shafts behind the wheel hex pins.
Apart from these things, the Bomber is a super solid and super fun platform.
The HD diff gears front and rear will never worry you, and the stock aluminium links are a big improvement over previous versions (with the exception of the rod ends). I've considered upgrading to steel/titanium links, but the stockers are still going strong and they are light, so I won't upgrade unless I actually manage to break/bend them.
The transmission gears are metal, however they are cast sintered/powdered metal and not true machined metal. There are machined metal gears available (Hot Racing), but I wouldn't worry about upgrading unless the stock gears end up failing. I'm running 3500KV Puller Pro power in my Bomber and the tranny gears have been holding up just fine.
I HAVE been through a couple of servos, though. The first one was an HH SHV500 that had a faulty centre pin and stripped the output gear during the above mentioned cartwheeling episode. The second was an RC OMG Servo which had some pretty impressive specs, but ultimately didn't even last a single run before that one was cactus as well.
Holmes was super cool though, and they replaced my SHV500 with a brand new one that has been going strong ever since.
If you stick to the tried and true, quality servos (HH, Hitec, Savox, Futaba), you should be golden.
Have fun, mate! "thumbsup"
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