This is a fairly easy job, done with basic tools.

Please put in Zerex G-05 coolant in, mix 50-50 with distilled water.
Zerex is typically found at NAPA, distilled water is from you local grocery store.
The capacity is in your owner's manual.

If your upper and lower radiator hoses are original, why not replace them while you have easy access.

When filling the system, be sure that there is no air in the system.
Tips:
Run the engine without the cap on the coolant tank when you are restarting the engine for the first time. Grab and squeeze the top radiator hose to 'burp' the system of air. Do not let your car reach operating temperature without the cap on the coolant tank. Be sure to run the heater at full blast to circulate the system and ensure the new coolant flows through everything. If you are willing to take your time on this, you may want to flush with 100% water first, drain, then refill with the Zerex, distilled 50/50 mix.

I am sure someone else will chime in, but it is straight forward, be sure to label or make a diagram on an 8.5x11 sheet of paper with the locations of the screws and whatnot you remove to ensure everything gets back to where it needs to be.

I don't know about Behr vs Nissens.

__________________
2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)