I think there is a very good reason why nobody has ventured to try and help you here yet.

I don't mean to come across as a smart a** or be gruff with you, but if you have to ask those kinds of questions, then you shouldn't be attempting this. You obviously don't yet have enough experience with the basics of building an RC plane. Had you built at least a couple of balsa kits (and NOT an ARF which provides little building skills), you would have an understanding of the construction of balsa and ply planes. My first plane 30 years ago was a stick balsa Sig Seniorita Kit, and after completing 3 months of building that, I still had to go back weeks later to correct mistakes I had made because I was inexperienced and didn't fully understand the instruction and pictures. I understood the mistakes after seeing other airplanes at RC clubs and hobby shop ceilings. At that point I knew how to work with balsa, glue, tools, covering, etc, to fix my mistakes. I was able to build more kits and then keep getting better and more advanced to build from plans and make major modifications if I wanted. Years later when I was fully experienced after having built a number of other planes, I would still go back in my spare time to modify things on that Seniorita that I didn't like. (besides the mistakes I had made early on and had already fixed). For example as I became experienced building a number of planes, I didn't like the fact the factory had me build the Seniorita with no compartment to reach the fuel tank. So I added a hatch. I also didn't like that it was 3 channel rudder control only....so I went back to add ailerons to the wing and make it 4 chan. I didn't like the rubber-band attached wing, and so I opened the wing again to modify it to a bolt on.... etc, etc. . I didn't understand things like "down-thrust" and "right thrust" of the engine mounting and learned later with experience how it affects the flight, as well as the importance of balance and minimal surface throws and-dual control for maiden flight. Eventually, many years later I converted the plane from fuel to electric, moving the firewall and adding air scoops to cool the battery, etc. Still have that plane today! These are all things you learn over time by building and also flying the planes. I assume that you already have some experience flying? (because you said that you already have .20 size engines, I assume you already fly?) That's good if you know how to fly already. But you still need to scrap your new plane-from-plans and buy a good high-wing trainer kit with good instructions that includes photos. Sig Manufacturing is a good brand for that. Just to make my point that you are trying to run before you know how to walk; electric airplanes are generally built lighter and less robust because they are designed to operate with much less punishing vibration of a fuel engine plane. So generally it is safer to convert fuel planes to electric, but not so much the other way around. Yes, you can beef it up, and move the firewall and things around, but it helps greatly to know what you're doing. You will also find that with electric planes (and plans for them) that they are generally shorter wingspans too. The shorter your wingspan, the less beginner friendly your plane will be because it has a higher wing loading. The rule of thumb is that planes over 60" fly better. I can vouch for you on that and prefer all my planes be 63" to 71" or so. Even bigger is better too (but is a PIA for me to store & transport) With experience too, you would know that you need to fuel proof your balsa plane for glow engines, but not for electric.

My final advice to you is to find a good balsa kit that is simple enough for you to build that you will still enjoy even though it's NOT those plans you had your heart set on. If you don't know how to fly yet, be sure to make it a high wing trainer and do the buddy-box thing.