hacer mediodía
'to take the midday break'
 

venta
'inn'
 

fuego
here, 'heat'
 

aparejado
'suitable'
 

alentarse
'to feel encouraged' (see also alentar).
 

tinaja
'earthenware jar'
 

manjar
'food'
 

mata
'bush, thicket'
 

poblado
lit. 'populated'; so translate as 'human habitation'
 

estar en su punto
'to be at its height'
 

ser menester
'to be necessary'
 

suspensión
used in the sense of 'wonderment' as well as 'suspense'; here 'delight', 'relief'
 

llevar la siesta
'to spend the siesta' (the siesta is such a well-known institution that there is no point in finding a more 'English' word).
 

alentar
lit. 'to give breath, life, to'; here 'inspires' (see also alentarse).
 

señora
an image: 'music is a great lady who does not give herself to anyone'
 

ingenio
'mind, intellect'
 

ello
refers to 'music', or, more precisely, to the bestowing of musical gifts
 

ella
refers to 'music'
 

ocupallos
modern ocuparlos; -rl- in such verb forms is frequently -ll- in the Golden Age (and the -ll- was pronounced like modern -ll-
 

arrebata
lit. 'snatches away'
 

habiendo salido...
The gerund is used here even though its subject (yo) is not the same as the subject of the sentence as a whole: this was a fairly common feature of the usage of the Golden Age gerund. The gerund often has a rather fuller meaning than is suggested by the English -ing form: here it may in fact have a concessive meaning ('although...'). In English, therefore, it will be better to translate using a finite verb construction: 'even though I had set out...'
 

ello
refers to me quedara.... Translate para ello as 'to do so'.
 

me quedara mil veces si hallara lugar...
Sequence of tense with si was different in the 16th century from today. The modern equivalent is me habría quedado mil veces si hubiera hallado lugar...
 

al mismo paso...
lit. 'at the same rate as I was going, it (the inn) receded from my sight...' Translate, perhaps, as 'as fast as I approached it, it seemed to get further away...'
 

no creí...
Be careful not to create an ambiguity in translation! 'I did not think I could get there until I heard the music...' might imply no creí que pudiera llegar a ella hasta oír (= hasta que oyera) música.... It may be clearer to translate as 'I thought I would never get there, when I heard...'.
 

siendo ella de suyo manjar tan sabroso para el oído
Compare the notes on habiendo salido. Translate: 'since it is in itself such sweet sustenance to the ear'
 

es de creer
lit. 'it is to be believed'; translate as 'you can well believe'
 

las pasiones del alma mitiga y suspende
Watch the word order: las pasiones is the object of mitiga y suspende.
 

por grandes ingenios que tengan
Revise this construction if you don't know it! It is still used extensively in modern Spanish as a way of making a concessive ('although...') clause: 'however great their intellect/intelligence'.
 

a quien
An apparently loose agreement: quien refers to aquéllos. But quien was still used in the 16th century for modern quienes: the modern distinction between singular and plural is relatively recent. You may also find quien referring to inanimate nouns at this time.
 

habían de enseñar
A modal use of the imperfect which is the equivalent of the conditional (you will come across this today quite often in speech). Translate as 'they should teach children' (don't forget that a passive could also be used in English here: 'children should be taught').
 

porque
corresponds to modern para que as well as porque (you can tell which meaning porque has by the mood of its dependent verb)
 

por
Like the por of porque, this sometimes has a purpose meaning at this time.