Mine is very discreet
but I am missing 4 flags so it might get bigger
The dilemma is,
when ? if you don't have it done within a month of the IM, you want to start training again and it becomes an issue for pool swimming as you are not supposed to go in chlorine while it is scabbed over.
where ? my suggestion is not where you can see it all day everyday or it will pee you off,
what to have, well there is many designs, I have a few on my website of ones done already for others as my bro is a graphic designer.
do I have the M logo or not - personal choice, as smithy says, its transcended the corporate issue now more as a badge of honour so to speak - but I do like his version of the Norseman tattoo 
Mine is my avatar, the only reason I haven't put the other 4 races on is that 2 of them are germany so am working on logo for Roth and one is Wisconsin, so do I do US flag or state mmmm,
And at the end of the day its personal but I would say go to a reputable place and of they don't ask you why you want it or question your logic and reasoning I would walk, most places have a duty to make sure that you are aware that this is for life ( unless you can afford 5 times the price to remove it lol)