Gun thoughts

Having two internal discussions going on currently. I am going to do two upgrade on my AR. First conversion to the A3 format with flat top receiver and magpul Moe forearm. This is a gunsmithing excercise as I am going to do the work myself and not just buy it. This will force me to get the equipment to do it. I am going to buy a new upper more than likely in 7.62x39. The reason is it is overall cheaper in cost for the upper, ammo, and magazines even with the need to buy and different bolt to handle military surplus. I am going to get the 20" barrel to try tonwring the most velocity of the round. I am also going to put a collapsable stock on it. The next is the need for a defensive shotgun for the house. I am looking at a .410 bore Saiga. I like the idea of detachable magazines and light recoil. Also there are some very good defensive rounds coming out because of the popularity of the Judge hand guns. Also will be getting my FFL next year as I am working on my gunsmithing certificate. Thoughts or opinions?