If you know you want to do ER without a doubt, then go for it! Aim to precept there.
One thing I know our school does is they make sure you have med/surg DOWN before you can precept in a specialty unit of any kind (ICU, ER, L&D, postpartum, peds, etc). Master those basics (ICU has a completely different skill set than med/surg) and show your instructors you can handle it.
Like you said, some places will hire new grads, some won't. It's good to get a feel for which hospitals run which way. In general, if you can get a couple of years of med/surg in, you'll likely have a better chance, but if you can precept there, you'll make key connections that will be very helpful if you're smart. I really hope to land a position where I'm precepting, and I'm letting it be known!