Easy investments would be in the starters. Buy Earthquake for Meganium, Ice Beam for Blastoise, and consider getting a Raichu instead of Jolteon. Cheaper to buy the second move, and while brick break isn't great, it's a fighting move, which can be very useful. Jolteon is stuck with electrics, so no subtlety or surprise, and it's not really worth buying the extra move unless you have Last Resort.
Ultra league team sounds solid, buy the poison move for FP Venusaur. Flygon is a beast, but is very specialized, maybe best not to lead off with it. Lapras is good, but expensive - Walrein is a good cheaper option, although without Ice Beam.
Have any BB Charizard? Buying DC is cheap, and very useful - great neutral damage if nothing else.
We're still learning about what's good and what's only fair. Have fun exploring it with all of us.