I am interested in the engineering and weights for aircraft around 8,059 lb (3,655 kg) Citation 505) and 18,900 lb (8,570 kg F-16).
Curious about specifically structural mass and landing gear systems. How much can landing gears lift?
I can point you at some reference materials you can use. These methods involve estimates for different types of aircraft and formulas you can use to estimate the component weight based on the MTOW and OEW, for example.
You can use the following books:
scholar.google.com is another good source for finding articles about landing gear systems and design in general.
Aeroplane landing gear is dimensioned for maximum weights, the weight data in OP is for empty weights. MTOW of a Citation II is specified as 15,100 lbs in Wikipedia, the F16-C as 42,300 lbs. From Torenbeek, Synthesis of Subsonic Airplane Design, category Light Aircraft.
There are two business jets listed with similar MTOW to the Citation II: the 1121 Jet Commander (now the IAI Westwind) and the North American Sabreliner. Empty weight of the Sabreliner is close to that of the Citation II and it is also a low wing mount, so I would expect the landing gear weight to be very similar = about 700 pounds.
For the F16: it is a fighter aircraft, with different design criteria than passenger aircraft. I cannot find freely available weight data for the F16, so a guesstimate would be based on the list of passenger aeroplane weight data in this answer for the VFW 614: about 1,600 lbs.