All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not permissible for the Imaam or the congregation to bend down during the Friday Khutbah (speech). However, if by “bend for few seconds” you refer to the sitting between the two Khutbahs, then this is the Sunnah during the Friday Khutbah. Indeed, the Prophet used to sit between the two Khutbahs. However, it was not reported from him or from the companions that there is a special mention of Allaah at this precise time; after investigation we have not found anything about this. What we came across is that this is the hour of the Friday prayer during which the supplication is answered. The evidence is the Prophetic narration which reads "…(the hour during which the supplication is answered) is from the time when the Imaam sits (between the two Khutbahs) until the establishment of the Friday prayer." Hence, when the Imaam sits between the two Khutbahs, the congregation may seek the forgiveness of Allaah, each one individually and secretly to themselves. For more benefit, please refer to Fataawa 88971 and 85862.
As regards the sufficient amount of exaltations on the Prophet in Tashahhud, then according to the Shaafi'i School the sufficient mention is to say "Allaahumma salli 'ala Muhammad", and anything more than this formula is only recommended, as stated by Imaam An-Nawawi, may Allaah have mercy on him. Allaah ordered us to exalt the mention of the Prophet but He did not specify the formula of this mention, so it was a general order.
With regard to reciting something else other than the Quran, then you should know that what is permissible in the first two Rak'ahs is to recite a chapter after Al-Faatihah, and it is not permissible to recite anything else than the Quran.
If a person recites anything else other than the Quran, then if it is a legislated mention or supplication which is permitted in the prayer, his prayer does not become void even if he deliberately recited it; in this case he may prostrate for forgetfulness.
For more benefit, please refer to Fatwa 81875.Allaah Knows best.