i've got four and differen't age gaps between each... i think there are pros and cons for any options... and then there is the whole it never happens when you are planning (which, it never did with any of ours lol, so really the whold drink a little too much and see what happens, may be the best route!)
so between my first two i have almost 3 years (april baby and then gareth turned 3 in june):
this is sort of the "ideal" spacing i think for a lot of people the big brother is old enough to "get it" but still young enough to play... i think the only thing about this spacing is to remember that a 2-2.5 year old is still a toddler... so they are pretty needy still, it can be a bit of an adjustment for everyone, and it can make for an exhausting pregnancy (imagine lugging yourself, your big belly AND your big toddler up the steps because they just decided they no longer will walk as two yearolds often do) also, everyone WANTS to think that a two and a half year to three year old will be potty trained so you'll only have one in diapers... but likely you will have two in diapers and be too exhausted for a bit to do any potty training.... and if you have already done potty training i think that at this age range reverting is really likely because they are still so young you know? (i always say a 2 year old potty trained is really actually a potty trained PARENT

)
Between my second two i have 16 months, it took us about a year the first time to get preggers, so we started early trying this time, and it happened... the fist shot we gave it...
this spacing is crazy hard... seriously, i think i should be honest here, yes it is great now that they are getting older, and it is freaking awesome that they are starting school one year apart, and they are dear friends as they get older (when they aren't fighting eachother tooth and nail) but good lord, when they are little it is hard, i felt like every day was seriously some sort of a marathon when they were both young, it was like carrying changing feeding cleaning calming cuddling all the live long day LOL... and they both had a lot of needs at the same time... if you are of the mind that you hate the baby stage and just want to get it all over with all at once, then really close could be the ticket, but sometimes i'm sort of sad because i think i missed out a little on owen reeceys babyhood because i was running around like mad to keep up with them.
By far, the easiest spacing, has been this last one. Reece was three and a half when tennyson was born. Tennyson will only be 1 and a half when reece starts kindergarden this year. It was remarkably easy to keep up with an infant when my older kids were all pretty much able to take care of their own most basic needs (pee poo water sleep tv LOL what else is there right??)
Personally I think this is the furthest spacing i would ever want though. I feel almost like I'm starting all over again with baby T.... the first set of kid is all off to school this year and t is just coming into his own around the house... i can't imagine them being even further apart, i would feel like i was at this mom thing for centuries no doubt LOL
ok... theres my novel!
just DO IT... thats my advice... yes you are right, you will never be 100% READY but i think brothers are the biggest gift i give my kids, because someday i am going to get old, and i'm going to get die or become senile or something... someday their dad and i will not be here for them, but i'm not worried, because when i'm gone, i know they won't be alone, i'm glad that they have eachother.