Presumably by Darbar Sahib, you mean Sri Guru Granth Sahib and by "sanchian" you mean Sri Guru Granth Sahib in 2 volume editions as published by SGPC.
If the presumption is correct, then certain pointers to your questions are:
a) "sanchian" have been designed to enable beginners to be able to read the Sri Guru Granth Sahib, without requiring as much seva as is normally required for Siri Guru Granth Sahib. For instance, there is normally no formal prakash of or Sukhasan for the "Sanchis", whereas for the Sri Guru Granth Sahib that is mandatory. "Sanchian" can be stored in a cupboard whereas Sri Guru Granth Sahib must only be put for Sukhsasan in a bed or at least in a palki Sahib.
However, as the text of the Sanchian is the same as that of Sri Guru Granth Sahib, while reading from the Sanchis we must be seated on the ground, without shoes and have the Sanchis placed in a small wooden structure in front of us, in an environment where no food or drink is being served so that the reader can focus on the shabad in the sanchian.
2. The life history of the Sikh Gurus and the shabads in Sri Guru Granth Sahib make it very clear that for all Sikhs every day of the month / year is as good as any other. There is no special place in our faith for Sangrands or Purnimas (this may surprise you as in quite a few gurdwaras there are a lot of Pakhands associated with these days). Yes, at the beginning of the month, it is common to read the Bara Maha and the specific sloak for that particular month and seek the Guru's blessings for that month...this is called reading the mahina (=month) ...but this is to be distinguished both in nomenclature and observance from the Hindu Sangrand (where Sangrand is a more auspicious day than other days)...Similarly, Poornima, or full moon is a day with no specific significance for us...it is a day to remember the creator just as any other day.
3. Finally on the issue of prasad, ideally you should work towards a situation where in due course of time you have the prakash of Sri Guru Granth Sahib at your house or at a gurdwara close to where you stay. You could then be able to do the full seva of the Guru including preparing the kara prasad. If you are very keen on having kara prasad served after your daily / periodical reading of the "Sanchian" you could prepare it with reverence, keep it by the side of the Sanchia, read the Sanchian and after finishing the reading, say an Ardas and distribute the kara prasad.
I would encourage you to work towards the goal of having a prakash in your house / gurdwara close to your house. However, till such a day arrives, please do read and vicharao the shabad every day through the sanchian..
May the Akal Purakh continue to guide you as you embark / continue on your spiritiual journey...remember the shabad enshrined in the Sri Guru Granth Sahib has come directly from the Akal Purakh..so if you can merge your "shurti" (consciousness) with the Shabad you will be taken straight to the Akal Purakh....and, believe you me, the glow and brightness in that Darbar will put the glow from a million suns to shame...