Is doing the Tawaf  circuits consecutively Essential?
Question

The iqamah for `Asr prayer was given after I had finished the second circuit of Tawaf when I did `umrah, so I prayed `Asr, then after praying I was not able to continue Tawaf because of the crowds, so I left with my family, and I came back the next day and did seven circuits of Tawaf around the Ka`bah to replace the five circuits of Tawaf from the previous day.

What must I do now because of having done nine circuits of Tawaf instead of seven? Is it essential for there to be continuity between the circuits of Tawaf, or is it permissible for there to be a lapse of time between them?
Is there a specific book which explains all the rulings on Hajj and `umrah?
Praise be to Allah.Is doing the Tawaf  circuits consecutively Essential?
Doing the Tawaf  circuits consecutively is a condition of it being valid, according to the most correct scholarly view. However, a brief interruption between them does not matter. 
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said: 
“One of the conditions of Tawaf being valid is continuity between its circuits.” (Al-Liqa’ Ash-Shahri, 3/205) 
Interruption of Tawaaf for Prayer
If the Iqamah for prayer is given when you are doing Tawaf , then you should pray, then complete Tawaf from where you left off in order to pray. 
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said: 
“If the Iqamah for prayer is given whilst you are doing Tawaf , whether it is Tawaf for `Umrah or for Hajj or a voluntary Tawaf, then you should interrupt your Tawaf and pray, then go back and complete your Tawaf. You do not have to start all over again; rather you may complete your Tawaf from where you left off, and there is no need to start the circuit over again, because what you did previously was based on a sound foundation, and it is allowed to interrupt it for the prayer, so it cannot be invalid.” (Fatawa Nur `ala Ad-Darb, 12/2) 
Shaykh Salih Al-Fawzan (may Allah preserve him) said: 
“One of the conditions of Tawaf being valid is that there should be continuity between the circuits, and one should also persist in doing a single circuit until it is complete. However it is permissible, when there is a valid excuse, interrupting that continuity , such as if the Iqamah for prayer is given when a person is doing Tawaf. In that case he should pray, then when he has said the Taslim, he should do the remaining circuits of Tawaf, carrying on from where he left off. The same applies if he feels tired during a circuit, and he rests briefly, then continues. There is nothing wrong with that, in sha Allah, because it is for a valid reason. But if he interrupts that continuity when there is no need to do so – for example, if there is a lengthy interruption between circuits – then in that case it is essential to start Tawaf all over again, because he did not fulfill the condition of continuity between circuits , with no valid reason.” (Al-Muntaqa min Fatawa Al-Fawzan, 67/1) 
Based on the above, what you did of repeating Tawaf in full, with seven circuits, on the second day, was the right thing to do and was what was required of you, because you did not complete the first Tawaf within a reasonable time, and you left a lengthy interruption between the two Tawafs. So it would not have been correct to try to complete the first one by basing the circuits on the second day on it. 
Shaykh Ibn `Uthaymin (may Allah have mercy on him) was asked: 
A man did two circuits of Tawaf, but because of the crowds he came out of Tawaf and rested for an hour or two, then he went back to do Tawaf again. Should he start all over again or complete his Tawaf from where he left off? 
He replied:
“If the interruption was lengthy, such as one or two hours, then what he must do is repeat his Tawaf. But if the interruption was brief, it does not matter. That is because with regard to Tawaf and Sa`i, it is essential that there be continuity, which means doing the circuits (or laps) one after another. If there is a lengthy interruption between circuits, then the first circuits are rendered invalid, and he has to start Tawaf all over again. But if the interruption is not lengthy, such as if he sits down for two or three minutes, then gets up and completes it, that does not matter.” (Majmu` Fatawa wa Rasa’il Al-`Uthaymin, 22/293) 
Recommended books on Hajj and `Umrah
Some useful books that explain the rulings on Hajj and `Umrah are the following: 

At-Tahqiq wal-Idah li Kathir min Masa’il Al-Hajj wal-`Umrah waz-Ziyarah by Shaykh Ibn Baz (may Allah have mercy on him)
Manasik Al-Hajj wal-`Umrah by Shaykh Ibn `Uthaymin (may Allah have mercy on him)
Al-Minhaj fi Yawmiyat Al-Hajj by Shaykh `Abdullah ibn Jibrin (may Allah have mercy on him)
Awdah Al-Masalik ila Ahkam Al-Manasik by Shaykh `Abd Al-`Aziz ibn Muhammad As-Salman (may Allah have mercy on him)
Tabsir An-Nasik bi Ahkam Al-Manasik by Shaykh `Abd Al-Muhsin Al-`Abbad 

And Allah knows best.