Hall, NA, Conover, Romney
Each brings something different.
Hall is dynamic, can come in and raise the level immediately, but also obviously has injury risks.
Conover has the most long term upside, but the least experience. The hope is that he forces the issue over the next 6 months and establishes himself.
Romney is safe without a ton of upside. He's a great backup to have (especially if Hall is hurt and Conover isn't ready)
As far as system goes, any coach should be able to adapt to their talent so not going to worry too much about it.