There is no problem with it if the mosque is not decorated with gold and the picture of living creatures and on the condition that it does not lead to extravagance and the wasting of resources.
Precaution demands that the permission of the custodian be obtained but if the custodian of the mosque disagrees with what is in the interest of the mosque or he doesn’t pay attention to them, the board of trustees can obtain the permission of the religious authority in that matter.
There is no issue with it.
According to some traditions, this phrase has been recited as a part of the call to prayer since the age of the Infallible Imams (‘a) but it was not widely recited in that era. Later on it became the motto of the Shiʻa school (for more information, refer to the valuable book of “al-Mustamsak”, chapter on adhān and iqāmah).
If it is not too difficult for them, they need to perform their prayers in standing position, even though they do it by using a cane and the like. However, if it causes them much difficulty and discomfort, they can perform their prayers in a sitting position.