Eagle1,
The normally quoted Vs data (a la POH/AFM numbers) are for 1g slow pitch rate approaches to CLmax alpha. If we look at Vs variation with GW, it generally follows something along the lines of square root GW. If we now look at an acceleration other than 1g, then we ought to be interested in the product of load factor and GW, ie nW. I guess that you could think of this quantity as being some sort of 'effective' gross weight.
Va is the most critical of a number of design cases to be considered but, in general, the limiting case usually ends up being that where, with
(a) limit load factor (that acceleration for which the GW structure is designed and tested to demonstrate that it doesn't bend too much), and
(b) MTOW,
CLmax arrives. The significance is that, up to Va, the hamfisted pilot has a degree of protection against his absence of TLC - remember how your initial instructor used to exhort you to treat the aircraft like an elegant lady ? ... good training in life skills for a young chap ...
If you now reduce the GW, then you could increase the load factor to keep the stall occurring at the same Va speed. However, this would then impose, potentially and probably, excess attachment loads, in particular, on the various bits and pieces bolted on here and there throughout the airframe.
As to your second question, the loads are normally measured in newtons, kilogrammes being a mass unit, although we are all comfortable with thinking in terms of kilogrammes as being a force unit. The load factor is the vertical acceleration factor compared to the 1g case as illustrated above .... It might help in your coming to grips with this idea if you consider the case of a lump of something on the end of a bit of string. With the string held stationary, the lump hangs down and you feel its 1g weight. Now, if you swing it around your head, the tension load in the string increases above the previous 1g load. You can think of the ratio of the two loads as being something analogous to load factor.
Did I succeed in making anything easier to understand ? .. or did I just muddy the waters further ?