Fantastic work mate!!! Love your painting and PE work!
Your first 1:48th... what scale did you work before this? I'm guessing 1:72 by your detail painting...
Ultimate...you can get model kits of just about anything these days, most commonly in the form of unpainted plastic parts in boxes, which you build up and paint from instructions. Balsa wood and other kits are also available, aswell as some 'ready to assemble' fully painted plastic kits. Kits come in a range of scales, aircraft for example usually 1:144, 1:72, 1:48, or 1:32, though there are some exceptions.
Most of us here get the usual unassembled plastic kits which require assembly with glue, and we usually modify or correct them depending on accuracy or subject. This can be done by 'scratch-building' (using home-made or spare parts), or getting 'after market' sets: vacuum- formed ('vacform') plastic, resin, or metal photo-etch (PE) detail sets seperately produced to enhance kits. There's also alot of decal (marking/ water-slide transfer) sets available if you don't want to use the kit decals, or assemble kits to a specific theme.
Hope this is of some help!
If you have any questions on the subject, just ask any of the guys here - remember, no such thing as a stupid question, only stupid answers!
Evan