I'd do a typical fold-over airfoil for something close to 600 grams. Also, what style plane are you wanting this to be? Unless you're looking to do 3D flying or advanced sport flying, a flat or symmetrical wing isn't necessary.
Just a little trick when using large panel type wings.
You can stiffen the FB massively if you paint the bare FB in PVA glue. Paint both sides at the same time and try to have both sides dry at the same time, (top and bottom of the wing panel).
I built an OTTO out of the "Otto Vs Eddie" plans, (A pair of depron biplanes), and I must have crashed it 10 or more times including a number or treeings and the high speed cartwheels. Whilst the wings were ripped off a number of times, each time I just had to glue the wings back on and it was ready to go.
If you are going to paint the PVA is an excellent surface!
As per normal I recommend that if you are going to try it practice on a few scraps first.
There are many ways to strengthen flat airfoils. I have used wooden dowels and carbon fiber to strengthen flat and KFM style wings and they have flown and held up well. I like using wooden dowels inset into a V shaped channel into the leading edge of the wing. It makes a nice smooth leading edge. If you don’t want the wooden to show you can cover it with a wide strip of paper pealed from scrap foam. I also like cutting a vertical line only going through one sheet of paper in the bottom of the wing. Then I open it up a little with a credit/gift card. I lay the carbon in vertically and after test fitting it, glue it in. Again, you can use scrap paper to cover it. You can also strengthen the flat airfoils by ironing the edges, there are some cool videos on YouTube on how to do that.
As long as you have a good method for strengthening the wings(as others have recommended some very good ones here), a mid size or larger plane with a flat plate air foil could perform well as a casual cruiser or slow flyer. I would not use a flat plate wing on anything I intend to fly at high speeds, whatever size or scale(flat plate wings have sketchy pitch stability and some handling issues when they get up to higher speeds). The under cambered wing is probably the best compromise between weight, effort/difficulty, performance, and durability for most general types of slow flyer plane.
Some form of KF style air foil is an easy construction method for solving the strength and pitch issues of the flat plate, but I actually would not recommend it for a dedicated slow flyer based on my own experiences. I've found planes with this style of air foil to lose a bit of performance on the low speed end of the flight envelope, although they are very sturdy as well as stable in flight(including at high speeds).
In a lot of circumstances I tend to like the flat plate style as well. Anything that isn't going for extreme speed and precision or has a wing shape that needs reinforcing, I tend to go with the flat plate. A recent little delta I made with a lazy KF airfoil flies pretty good, but for negligible amount of speed and stability I gained I should have just gone flat and it would have been abut the same with way better high alpha and less weight.