Bro, No one is knowledgeable or illiterate. We get everything from here and we leave everything here by sharing with others. Knowledge is knowledge. Either one have it or don't have it. To have it, you have to look for it. The first and foremost rule I learnt after gaining in life is, if you know something, grow it by sharing, never try to keep it to yourself and I think that's what this forum is for too.
Now coming to your question:
Use BSNL as Primary only if they have good network at your place and surroundings.
You can port to BSNL at local CSC center. For Rs.100 or even less depend on how much person want to earn, they will offer you Rs.249 FRC plan with 45 days validity with UL calls + 1.5GB/day data and 100SMS. If your usage is less than Rs.201 plan with 90 days OG validity and 300 mins calling + 6GB data will be sufficient. If usage is high then better go for Rs.1999 plan with 365 days validity and 600GB lumpsum data.
For Rs.50 they give you Rs.107 FRCplan when you port in, with 35 days validity and 300 mins call + 3GB data but no SMS. Even OG SMS will not work in this plan without balance.
You can also look at 1199 grace 2 plan (8th day after plan expiry) as I mentioned before. 24GB Data + 100SMS/day + UL Calls for 336 days. It will effectively cost you Rs.107/30 days for UL calls + 2GB per month data. You can then use data vouchers like 151_40GB_30 Days to add more data but BSNL has validity for data packs unlike Jio that adds it till main validity. 411 Plan has 2GB/day data for 90 days and can be used in addition to active pack. But confirm with CC for your circle as it may overwrite current plan. From My BSNL App you can llok for it as there they show whether you can use any plan with active plan or not.
If you recharge 1199 grace from Amazon RuPay platinum Friday offer same will cost you Rs.100 less @Rs.1099 effectively costing Rs.98/30 days.
There 797 Plan good if you want to keep number active as for 300 days. For first 60 days of this recharge you get UL Calls + 2GB/day data + 100SMS/day. Visit
https://portal2.bsnl.in/myportal/tariffs.do?PREPAID to get all details of plans.