AO is typically the entry level for an operator. There are a variety of other names for that position such as Nuclear Systems Operator, Plant Equipment Operator. Some also have a helper positions as entry level.
NLO may be the same as AO or some places have a position in the Control Room for operations of equipment which does not affect reactivity such as diesels, Rad Waste systems, etc.
RO requires an NRC Reactor Operators License. The position is also known as Control Operator. This position operates the controls which affect reactivity, i.e reactor and turbine generator.
SRO requires an NRC Senior Reactor Operators License and is usually a supervisory position, most places have one SRO per unit, with a Shift Manager over all units.
After one year you would be eligible for a SRO license since you have a degree, though you probably won't get the opportunity for several years.
I'm not up to speed on current salaries but at a guess
AO as you noted around $30/hr
RO about $40/hr plus some type of license bonus
SRO 125K/yr