So the thing is, you really should wait until the beer is fermented fully before you bottle it. The beer will ferment until it is done, regardless of when you bottle it, so if you bottle it too early, your going to have exploding bottles and all sorts of mess. So you shouldn't really think of bottling in terms of when you think it tastes good but more in terms of when it's ready to be bottled.
That being said, it's fairly likely that it is ready to be bottled, assuming it's been fermenting for about a week or more. The best way to know this is by taking gravity readings and waiting until they stabilized, but as long as it's been in for about a week and you've seen lots of bubbling in that time it is probably done fermenting.
You can bottle without priming sugar. There won't be a ton of carbonation but it won't be completely flat. If you do decide to carbonate, the priming sugar will have no noticeable impact on flavor or ABV (except that the beer will be carbonated). That's not to say that it will have no impact, but there is almost NO way you will be able to taste the difference.
If it's been fermenting for a while I'd say throw some sugar in and get it in some bottles! If you like it now then you'll definitely enjoy the final product and you can always crack some open early if you can't wait for them to fully carbonate, they'll just be a little flatter. Hope it turns out great!