planning my engine, need help

Why get an aftermarket block and go with stock displacement? If (actually, more like "when") I get an aftermarket block, I wouldn't consider anything less than 347ci. I'd actually probably go 363 or bigger.

The AFR 185s or TWs 170s are "big enough" for your power goals on a supercharged 306, but if you go to a 347, you'd be better off with something bigger, like Twisted Wedge 185 or 205 (yes, TW 185s are actually a "bigger" head than AFR 185s, don't let the numbers fool you).

The Cobra manifold will probably be your weak link in the end. The power goals on a supercharger with that intake are possible, but understand that it will be the bottleneck.

For the TB, again, the Cobra intake will hold you back on what you can do. I believe a 70mm will fit with very little or no port matching. A 75mm or bigger will probably require port matching. On EFI cars, you really almost can't go too big with the TB. It's not like a carburetor, we're not worried about velocity through it or anything like that. All you really want it to do is get out of the air's way at WOT.

For injectors, you'll probably want something around 42s. Take a look at this calculator:

Injector Size Calculator

You probably will not need aftermarket fuel rails for 400rwhp.

That combo is all over the place.
Make that dart block into a 347 for sure, use race heads like the cnc wedges or similar, good intake and you should be well over 400rwhp without the blower.
The way you are doing it, you are going to have to take the whole thing apart and do it again.

Then when you are ready for more power get a D1 or Ysi and then the hp will jump up to around the 650 range.

most people dont need to upgrade the fuel rails when building a new motor -but they certanly look better then the stockers. FWIW stock rails can support 700+hp

A safe number to expect the stock block to hold to is 450rwhp, some put up with more, but IMO, stretching it for a few more hp isn't worth the risk.
Don't go nuts on a 306 rotating assembly either, it's the block that's the weak link not the internals.
If you like though, consider a good 347 rotating assembly for the stock block, one that can be transferred into a race block in the future. Just remember though, if you crack the stock block, all the internals will be garbage.

TW's have been on sale at summit for $950 so check that out too, to save a few bucks.