How should I go about restoring my 72 Chevelle's 350 sb?

I have a 72 Chevelle with a 350 sb that has been sitting covered outside in Florida for the past 3-4 years. Before it began to sit I rebuilt the top end of the engine but then it needed some major body work and put me in a huge SNAFU. Anyways… I finally got the savings to bring it into a restoration shop, they got it running but said 3 cylinders had no compression and that it was leaking and burning fluids badly.

They stopped there and told me they would save me thousands of dollars and told me to go and buy a crate motor for the car.

I am thinking of bringing it home (I finally have a home with a garage again) and pulling the engine out myself and doing a rebuild slowly over the next year or so to make sure I do it right, and do it once.

Any ideas on this? I've added up an estimate of parts for a complete top and bottom end rebuild and it comes pretty close to what a new crate motor with 300hp would cost. However, if I rebuild it myself I would be able to spread the cost out little bits at a time over a year or two.

Time is not of the essence. I don't mind having a project like this again (I am pretty savy with mechanical issues when I have an interest).

Money is of the essence. I am a high school teacher with a mortgage and a baby on the way. I like the idea of spending little bits at a time on what I can afford rather than putting a $2500 charge on a credit card for a new engine.
Added (1). The restoration shop said they stopped at the point they did because they do not rebuild engines (they outsource that) and that they had no idea what would be causing the problems in my engine. They said it could be from a bad break-in with the last rebuild, or that the Florida humidity could have eaten away at all the seals/gaskets/bearings, or even as simple as valves/lifters not being tightened properly.
Added (2). Whatever the case with the engine, my plan is to bring the car home, remove the engine and put it on a stand where I could begin disassembly and start to inspect each part to see what all needs to be replaced. I would then take the block back to a machine shop to have it decked (it is already bored.30 over from the last rebuild) and also to have the heads looked at. I might just purchase new Vortec heads though just for the ease of purchasing matching components to specific brand new heads.

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