Now that I downloaded the MIDI file, I saw that it goes up to B (natural) above the staff. Definitely in the professional league.

You have a soprano voice, so you should not make the mistake to sing too much in the very low register. But transposing is absolutely legitimate, unless you are publicly performing as a sopranist (that's what Leadfingers seems to have in mind; BTW: even public performers are sometimes caught cheating; a professional orchestra must be able to transpose on the spot if the diva chooses to have a cold).

A metronome and a tuning device are two helpful tools for two distinct problems. Both are available as free software (though I cannot tell you authoritatively which software is good - ask the 'Cat). The same applies to MIDI sequencers that can transpose and slow down a MIDI file. I use a software that costs some 30 AUS$, to vary the tempo at liberty, thus addressing Bert's problem (- particularly handy for accompanying a choir).