There is considerable amount of modification becuase an H (and F) series trannies don't use linkage, they use 2 cables. Basically one cable is for moving forward and backwards, the other is for left and right motion. Honda's B and D series are rare using actual rod style linkage as cables are much more common (the new K series engines use cables I believe as well). They are much easier to package into the car but don't give quite as strong "feel" to the shifter. I believe most swap kits offer a mounting plate (probably at addition cost, but I don't know for sure) that allows you to mostly bolt the cables into place (there will probably still be some cutting and manipulation to make room for them).

Couldn't tell you on the downpipe, that type of stuff is pretty easy for a muffler shop to fix.

I would say not to if your planning to go turbo, consider it if your staying N/A. For a turbo setup, your much better off investing that money in strenghtening the bottom end, specifically the N/A designed and weak for FI pistons, rods and cylinder walls. Forged units and replacement sleeves will give you a much stronger engine. A stroked engine would probably make a little more power due to the increase in displacement but with a turbo, more power is basically a turn of a boost controller dial up and good fuel tuning. For N/A engine, it might be considered but if your on a limited budget, an aggressive set of cams and a good valve job will probably net a lot more gains. I would think of a stroker kit as more of a next level modification after all the basics have been done (just my opinion though).

As for LS vs VTEC. A turbo'd VTEC engine will make more power on the same boost. That being the higher lift cams and higher compression. The LS will be about $1000-$1500 cheaper, saving a considerable amount to invest into the turbo. Some people argue that the longer gearing LS tranny is also better, but for low boost setups, the more aggerssively geared VTEC trannies will make you faster. More aggressive gearing = faster accelleration, traction limiting. There are also issues with the extra overlap (the time both the intake and exhaust valves are open at the same time) in a VTEC engine hurting power. I've heard the issues isn't boost escaping into the exhuast, but actually the excess pressure between the exhuast valve and turbo can actually push back into the intake manifold heating and contaminating the incoming air/fuel mix. These are all issues you need to be aware of when considering your choice of base engines.

As for 300 whp, that depends entirely on what turbo setup you have and what kind of tuning you have done. That's going to be around 350 crank hp, which is over twice the stock output, so your probably not going to do that on a stock bottom end. 220-230 at the wheels isn't unreasonable for a good turbo setup and will probably get you close to if not into the 12's. Seeya.