BadDragon Toy & Purchasing Recommendations

Seeking toy and purchasing recommendations. I am relatively new to backdoor toy play. When I do play, I use an Oxballs Ergo plug S. I also own a Tantus Slik Large that I use infrequently and an exballs ergo plug M that is too big.

1. My first question is, should I purchase Small or Medium toy from Bad Dragon? I dont want to outgrow the toy too quickly but also don't want to buy a toy I can use cuz its too big. Do people who purchase S toys end up regretting not getting a M toy?

2. Second, the toys I am considering are Bishop , Vector , Echo , Rex and Nox. Does the community have a recommendation for the best one to get first from the models listed? Nox and Echo were recommended to me by a cam model, I like Bishop and Vector's cyber designs and I saw a recommendation that Rex can be used as a plug with its bigger knot. All of them have interesting

3. Should I buy second-hand, a flop from BD website or should I buy full price from BD website?

I appreciate all information and recommendations you guys have.