I have been working on a competitive team and I am worried that if I don't start at lvl.1 I won't get the most out of it. so does it matter if I train at lvl.1 or lvl.100? The ones I'm most worried about are my Togekiss and Vaporeon. I think I will put a RMT in later too. Thank you for your time and help!
Short answer: no.
What level you EV train at doesn't matter since EVs don't have anything to do with levels. In previous generations you gained the EVs after you leveled up but with super training you gin them instantly so it does not matter.
Hope I helped.