I have a Hobbywing combo in my 8ight-E 3.0. The 150a / 2200kv sensored combo.
You should be in the 2000kv and up range if you are going to race on a larger fast track.
I have had a Mamba Monster 2200kv combo, and also a cheaper TORO/Trackstar combo set.
I even have a Leopard Hobby 4072 2200kv motor, that is fairly cheap and is even more smooth and just as powerfull as the Mamba Monster 2200kv.
Many racers uses different Tekin combos, but Tekin is on the top of the pricing range, and the fact is that many low or mid priced brands performs just as well. The main difference is often no or limited warranties with the lowest priced brands, but you get the combo for half, maybe even a third of the price many just replaces if anything happens.
To have a good alround E buggy package, and if your wallet is not booming, I would much rather buy one of the lower priced combo brands and spend some extra dollars on a good servo, BEC's if needed, good radio etc.
As mentioned, I have tried low, mid and high priced combos, and I did not feel any difference.
That's why Hobbywing is so popular and used by many racers, it maybe, currently, offers the best combination of quality, reliability, performance and price.
You must decide on whether you want to run sensored or unsensored. A sensored combo does not only give you much smoother throttle control, it also offers smoother braking.
At my local tracks there seem not to be a favoured choice, some runs sensored and some not, which I think is odd, as sensored offers more refined control.
And there is the question of running 4s, 5s or even 6s. If you don't know go for 4s, as this is what the most racers use. In my part of the world (Scandinavia) I have only seen 4S use, but I can see that some US racers use 5s in combination with a lower kv motor. But if you do not want to dig into that, go for 4s.
And for batteries (lipos), many, many buy from Hobbyking.com. Lowest price and good quality. If you want to be able to use your lipos in most places, buy ROAR approved hard packs.