Create new ROM for Android Centora (with restricted apps and modified Settings apk)

Hello My name is Joel Schwartz I am working on a project to create a Samsung android phone with some restriction, for a school, (model is Sasmung Galxy Centora), since it is for a Scholl with children in the age of 15-18. The restrictions we want on the device are: 1) disable installing new apps 2) Remove all apps that provide internet browsing (like you tube chrome) Also very important “in app browsing should be blocked even for apps that are installed” 3) Need to modify the setting apk otherwise there is a way to access the web from the phone through the settings apk (for example by going to setting, about device, legal there is a link to [login to view URL] which can be used as a browser) 4) Developer option should be disabled (can also be done by modifying the setting apk) 5) whatever changes are made to the phone should not be changed if the phone is factory reset should be permanent 6) we are working now on a Samsung device, so we need recovery booting and “download mode” (most imported) disabled so user will not be able to flash any new rom ETC. to device (this could be done either by: disabling volume up button until the devices boots up {hard ware}, or by By editing the SBL Second boot loader (this is handling the booting process, which is based on little kernel Clcik here for Link or by disabling download partition. 7) add few apps that we need as system apps to the device We have done most of this in the past with an LG device that didn’t have download mode, we rooted the devices and edited the settings apk and removed all stuff that we didn’t want and added our apps as system apps and it worked very well.. However now with the Samsung device we are having issues with disabling download mode, also we are having issues editing the settings apk, once we edit the apk it is not showing on the device (but will be seen in the system/app/ folder, we tried alsready changing all premissions.) I think it is an issue with the app signature since is it using permission as “ndroid:sharedUserId="[login to view URL]” and it is not singed with the same key as the phone. So we looking for someone that could help us out with problems mentioned above. Waiting to hear from you...