Firstly welcome back to the sport ... a hell of a lot has changed, I've been racing since the mid 80s and more has changed in the last 3 years or so than the previous 23!
I think LiPo's have been covered well, all I will add is that it's not worth getting hung up about having huge C rating cells as there is no "standard" I can find to determine it.
It is absolutely the case that you can get cells with the same capacity (say 4600mAh) and different C ratings (say 30C and 40C) from different manufactures which will perform the opposite way to expected.
The theory is that the C rating is absolute max discharge loading the cells can give (so 4600*30C = 138000mA or 138A if you prefer).
Other things influence this, not least the load across the cells whilst the test is happening.
So if your comparing two different Orion cells then the C rating is likely to be meaningful, if it's an Orion and an LRP it might not be quite so clear cut.
The biggest single thing with the LiPo cells is the power delivery is brutal and consistent, no drop off as the load increases or the charge depletes.
Brushless motors, they WILL take some getting used to. Basically as a rule of thumb (definitely not and equivelence factor though) you would use an 8.5 in place of about a 14/15, 7.5 in place of a 12/13, 6.5 in palce of an 11 and a 5.5 in place of a 10 turn brushed. As I say not exact but a go approximation.
The other thing to remember with brushless, and something I only really got to grips with at the back end of last season, is that the old rules of "mild" & "wild" motors no longer apply. In the old days if the car was a bit of handful with an 11t in you might change to a 13t to calm it down.
With brushless I have found (thanks to Matt Dodd's advice) that actually now you go the other way! Let me try to explain, the high wind motors (say 8.5) may rev less and give less power in terms of W but the way they do it is with brutal torque where as a lower wind (say 5.5) will rev more, and have more watts but it will have less low rev torque.
The gearing range is quite wide on brushless motors compared to brushed so you can match speeds via that route and have the bottom end characteristics from the low rev torque of each motor.
For example I have a 5.5 in both my 2wd and 4wd cars and a 6.5 on it's way for tracks that need a little more immediate grunt (say an awkward gap jump following a slow corner or similar) and I used to run circa 12x2 in 4wd and 13x3 in 2wd.
The other thing with brushless is the ESC is far more important than it was in terms of smoothness as now it is the ESC which controls the ramp rate of the motors not the abilities of the motor itself.
The smoothest ESCs I have found are the HobbyWing (rebadged as Speed Passion and a couple of other brands too but at much more money than buying a HobbyWing branded one) and the Tekin. Whilst I like the Tekin (it's tiny) I can't get over the fact it's twice the price ... 2 for 1 can't be overlooked IMHO!
Tuning brushless with rotors has been mentioned. I'm no expert, but the theory is more air gap (smaller OD on rotor) is more revs, less torque, less efficiency; opposite is being true ... this mainly applies to the mid and top end range though when the motor is already spinning. Larger ID on the magnet giving less low end and vice versa. As I say, no expert.
Chargers have been covered, basically anything branded from a UK model shop is likely to be fine ... buyer beware if you insist on buying outside the UK.
As has already been said the days of aluminium and titanium screw kits, the thinest carbon parts and drilling holes in stuff has passed. Whilst the minimum weight limtis are still the same the cars are running fatter, 2wd cars typically coming in around the 1650-1700g mark (1474g limit). Have a look at the Rudebits website to see the typical ballast we carry around.
I have just been working with a guy who is coming back to racing after 15 years away and he was blown away with the punch of the current power plants (and most racers say my car feels soft as I've tuned the agression out) but also how strong and reliable the cars have become. In case your interested in what he has chosen to use it is HobbyWing ESCs and Kyosho cars, will be going to Orion power very soon.
I think the thing you will find the most suprising is that with all the other advances we are still running the same tires as we were in 90s!!!!
I hope that has been of some use (by the way ... what are you running in the front of the Mk2, 20vt?)
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