I am only a week or so into learning the banjo and I am going to try a four string banjo but tuned to G. I understand most four string are not tuned to G and called tenor banjos. Also I think the string spacing will help. Is this tuning (G) uncommon in a 4 string? 
Regarding string spacing
In short, yes.
You can do anything you want with an instrument but you may have trouble finding resources, like written music or advice, if your instrument is unique.
When you say ‘string spacing’ do you mean scale, that is the distance from one fret to the next?
Usually string spacing is about the lateral distance from one string to the next. A tenor or plectrum neck should not necessarily have a wider string spacing that a 5 string neck. However, a tenor neck is shorter than a 5 string so the scale is very different.
— Begin quote from "bluenote23"
When you say ‘string spacing’ do you mean scale, that is the distance from one fret to the next?
Usually string spacing is about the lateral distance from one string to the next.
— End quote
I meant the gap between strings, more room for my fingers.
I see you’re also asking similar questions on the Banjo Hangout.
I don’t have a lot of experience with tenors or plectrum (long scale 4 string) banjos except for a cheap asian tenor I once had and the original neck of my converted plectrum but in neither case was the string spacing any wider than the 5 strings I have now. The plectrum was a very old vintage banjo and had a really skinny neck so the strings were more cramped than on my 5 string.
But ask the same question about string spacing on the BHO and you should get a more informed response.
With a tenor, if you tune in open G, because the scale is very short, you may need heavier gauge strings because you’ll be tuned lower than usual and the strings will be too slinky.
I don’t know if you have already bought your banjo but the online resources in terms of instruction and repertoire are fairly limited for 4 string banjo compared to the 5 string.
— Begin quote from "bluenote23"
I see you’re also asking similar questions on the Banjo Hangout.
I don’t have a lot of experience with tenors or plectrum (long scale 4 string) banjos except for a cheap asian tenor I once had and the original neck of my converted plectrum but in neither case was the string spacing any wider than the 5 strings I have now. The plectrum was a very old vintage banjo and had a really skinny neck so the strings were more cramped than on my 5 string.
But ask the same question about string spacing on the BHO and you should get a more informed response.
With a tenor, if you tune in open G, because the scale is very short, you may need heavier gauge strings because you’ll be tuned lower than usual and the strings will be too slinky.
I don’t know if you have already bought your banjo but the online resources in terms of instruction and repertoire are fairly limited for 4 string banjo compared to the 5 string.
— End quote
Yeah, I seem to have got myself involved with two forums. I am asking all I can because it is all a bit complicated. I do appreciate that 5 string playing seems well supported.
As for spacing it is because I used to play bass (guitar) and so two finger plucking banjo I was hoping would be a logical progression.
Helijohn: do yourself a favor and get a 5-string. It seems to me that playing a tenor banjo is one step up from playing the ukulele. I’m not really qualified to give my 2-cents’ worth about banjos, but at the risk of speaking without knowing what I’m talking about, I really think you’ll be happier with a 5-string.
— Begin quote from "Julian"
It seems to me that playing a tenor banjo is one step up from playing the ukulele.
— End quote
It is sort of why I want to tune to G and go 4 string. Uke conjures up visions of strumming. I want to learn finger picking.
It was a uke-banjo that started me playing when I was a kid but I never really liked the uke style of play so got a jazz guitar.
I now have a 22 fret 4 string which I am going to string as in a 5 string and the width of the neck at the 22nd fret is the same as for the 5 string I have. However, the bridge has the same spacing as for 5 string so the extra width available on the neck with having fewer strings is not being taken advantage of. Bridges are nice and cheap but the slots are pre-cut. Does anyone have any suggestions on making a wider slotted bridge?
Buy a bridge w/out the slots cut in in or have one custom made to your measurements.
There are many who make banjo bridges and sell them.