Hello machinehunter, welcome to AF
1/24th seems to be the most popular scale around these parts. It is my favoured one at least. It makes a nice compromise between size and detail. However there are other popular sizes, like 1/20th - for Tamiya Formula One cars; 1/12 - lots of detail but also take up lots of room and time; and 1/43rd - super small.
Regards painting yes brushpainting doesn't work too well for the gloss finishes on most cars, but is good for small pieces. However, if a brush is all you've got then go for it, we all have to start somewhere.