Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
No doubt that conveying the message of Islam to those who do not know about it is among the obligatory and distinguished acts of Shariah.
Allah Sent the messengers to spread the message of Tawheed. Allah Says (interpretation of meaning): {And We did not send any Messenger before you (O Muhammad SAW) but We inspired him (saying): Lâ ilâha illa Ana [none has the right to be worshipped but I (Allâh)], so worship Me (Alone and none else)."}[21:25].
This is proved in a Hadith from Rabeea bin Abbas who said: ‘I saw the Prophet (Sallallahu Alaihi wa Sallam) in Zi al-Majaz market who was saying: O! People say La Ilaha Illa Allah you will be successful”. He used to go along the streets announcing these words while people would gather around him and he wouldn’t stop talking, repeating the same call ‘O! People say La Ilaha Illa Allah’ you will be successful. [Ahmad, al-Arnawoot considered it as sound]
No doubt, all Muslim scholars and callers to Islam are advised to make use of all possible means to convey the message to all people. But the matters you are asking about consist of some unlawful activities which you should avoid.
1) Lying and fabricating lies concerning the good results of this act without having any basis from Qur'an or Sunnah.
2) Fixing the number of people to whom the message should be conveyed. As you know that determining the limitations such as numbers, etc. is a form of worship that could not be limited unless there is sound proofs of Shariah for that.
Once again, we emphasize that calling towards Islam is a good task and the one who carries out this job will be rewarded by Allah (Subhanahu Wa Ta’la) in this life and the Hereafter.
Allah Says (interpretation of meaning): {Let there arise out of you a group of people inviting to all that is good (Islâm), enjoining Al-Ma'rûf (i.e. Islâmic Monotheism and all that Islâm orders one to do) and forbidding Al-Munkar (polytheism and disbelief and all that Islâm has forbidden). And it is they who are the successful.}[3:104].
Know that encouraging people on doing good and preventing them from committing evil should be through what is proved in Shariah.
As for what people do by ascribing huge rewards for some good deeds and limiting the way of carrying those deeds without any basis it is not correct; one should avoid it and should not believe in it.
Allah knows best.