Don't scrap legendaries, convert those to scrip at the machine. Scrap everything else you might want plans for. If you get the Handmade Gun plan, you can build one on-level at level 35 which would be perfect, but of course you want to be able to trick it out with modifications if you can. I forget the price I paid, but it is earlier in this thread. I think it was around 6000 caps for that plan from one of the vendor bots at the Mall.
If you struggle to get a new gun, I can build you one. I have the Handmade and Fixer plans among others.
To achieve anything in this game you must be prepared to dabble in the boundary of disaster — Stirling Moss