Hello everyone, I am brand new to this forum, and bonsai in general. I am hoping to get opinions on starting a new juniper bonsai in early july/summer. Everything I’ve read On here so far said that this is not the ideal time. But nothing I’ve read has really said that you can’t. Is it reasonably possible that the tree would live, or should I definitely wait until late winter to repot, wire, prune roots etc.. Thanks in advance for any info!

Wait.
Keep it outdoors.
Water properly.
Get to know your tree first.

Well.. As creating a bonsai is a proces taking several years / decades, getting a new project going can be done now. Look for a tree. Search around till you have the perfect species & shape. Then start looking at the design options, and perhaps thin the tree out a little bit. Then, in late summer, you can take the first steps shaping it. Come spring time, you may consider a repot, if it is strong & did not see any die-back from your wiring.