1) FatDaddy modders connector
2) Keystone battery sled (order online from Mouser)
3) Again order online from Mouser (200g or close tactiles are best)
4) Fasttech has some great mod enclosures, search on power banks or enclosures.
Fuses can be confusing, but fortunately there's no difference in using them for parallel 18650s or 26650s. For parallel cells, the best thing to do is use a fuse on each cell. That way you have protection from excessive equalization currents if you happen to insert cells with a large charge mismatch. Just one fuse on each cell is fine. I would recommend not using more than 2 fuses in total for any application since there are derating issues that come into play when using more than 2 fuses in parallel.
The DNA 30 has a maximal input draw of 12 Amps. Since the load is split between the cells, each cell has to provide 6A so you would use a fuse with a 6A hold rating. Though, you can go a bit lower than that if you need to. PTC fuses have a hold rating and a trip rating. The trip rating is usually about double the hold rating. You can go about halfway between the two if you need to so you can use fuses with as low as a 4A hold rating.