If you want to go with the butt edges and rectangular nails, the cracks should not change appreciably from T&G. Are you going to put it over a subfloor? If not, you could have big problems with drafts and dust migrating. The other thing is that with the rectangular nails, you will have to reset them when you need to refinish. I don't know enough about shiplap to really comment.
For what it's worth, you can mill the tongues and grooves with the $60 Sears router and a table goes for about $40-60 and you can sometimes get a deal on both for about $100. Then you can get the bits for $30-73 from MLCS. A lot of work and a lot of chips, but could be fun. Henry in MI