Historically ship models were made mostly in 1/8 (1:96) or 1/16 (1:192) scale. These were mostly wooden models. As injected plastic became economical to use there were more "box-scale" kits - i.e. kits who's scale varied to fit a standard sized box. In the sixties a consortiuum of Japanese model manufacturers decided on a common 1:700 scale for their waterline ship models. One of the reasons that that has been postulated for that scale was the size of Japanese homes. Airfix decided on 1:600 scale, other European manufactures decided on 1:400 scale. Later 1:350 was introduced as twice the size of 1:700 (actually 8 times the volume). 1:72 scale and larger has been used for selected smaller subjects (PT boats, Corvettes, etc). Lately there has been a growth of make it bigger and some fool will buy it - even if he doesn't have space for more than one.
RC scales have continued to be in 1:192 and 1:96 due to the size and weight requirements of the radios and motors. There have been some 1:48 RC hulls (twice 1:96 scale) but they are expensive fiberglass items which require you to scratchbuilt everything from the deck up. Plan on it taking a year of more to complete each one.
If you are looking for a wide-ranging collection of ships, armor, and aircraft which are common in scale you could do a 1:72 scale PT boat, Sherman tank, and B-17. You will be able to find a couple more ship options in the patrol-boat/corvette -sized craft - but generally nothing larger. 1:48 scale - the ship pickin's get slimmer except for the bare RC hulls. In 1:32/1:35 scale you again fall into the patrol-boat subject with nothing larger.
I would suggest that if you want a wide ranging collection of ships of several classes you go with the more popular 1:700 or 1:350 scales and build everything in that scale. To delineate the scale size differences use some human figures (yes they are available in those smaller scales) to illustrate the size differences between your 1:48 scale pilot and 1 1:350 scale crew