I would stay its a bushing. I would go through all of then in your suspension. Remember you have a 20 year old car and rubber and plastic deteriorate over time. I would also definitely shop around for another shop.
The cheap one will hold whatever pressure its rated to but it most likely break down fast and break. As for the fitting as long as the new line is similar it should work. I was always had problem putting brand A fittings on brand B hose.
To get better mileage make sure you stay up to date on your maintenance, make sure your tire are inflated to the right air presser and change your plugs. It also helps to keep your air filter clean.
From all the looking I did on these no one had anything good to say about them. Here is a link with your same question. http://www.dsmtuners.com/forums/bolt-tech/457341-smartfire-injectors.html
You get what you pay for.
I would figure out if your block is still good and do forged internals if your power goal are over 400. If you plan to build it yourself do a lot of research first.
Make sure to remove the 2 bolts on the drivers side bearing carrier and I use a thin pry bar between the trans and the cvc shaft. You should feel a pop and it will move freely.
I would go with a 5.3 and turbo it. The 5.3 is a great motor that will take a punishment. I 270,000 on the one in my old truck before trading it off. They can be easy found in most junk yards.