Changing gearing by sprocket sizes

[Jez]

I need to replace my sprockets on my 2003 Gen1 thou and I am thinking of lowering the gearing. Is a tooth down on the gearbox sprocket too much? Is the chain long enough to fit round a 46 tooth rear sprocket? Will it make the bike feel any different? Any thoughts in general?

BTW what is the size of the sprocket nut, please? Just need to make sure I have all I need before I start.