For the lens, I personally wouldn't bother with a monopod unless its weight is going to be an issue for you when you're out shooting for hours. If you still desire a monopod, then I wouldn't get the bottom flip-out feet which is more designed for video than photography. It just adds weight and cumbersome in a crowded or tight spaces.
If Gitzo is too much $$$-wise, you might want to look at some of Sirui monopod options. For monopod, I wouldn't use a ball head. A tilt head is better for birding and wildlife, and contrary to conventional wisdom of many folks on this forum, I really recommend a tilt head WITH the panning base. What you end up then is essentially a monopod with a gimbal head, the most ideal set up for birding and wildlife. Of course, you DON'T need a panning feature in a head for monopod since you can simply accomplish the same by physically twisting the monopod side to side. However, I found it's whole lot better panning than physically twisting and it's so much smooth just as with a gimbal head. There's also less likelihood of wearing out the monopod rubber or losing the spike foot from constant twisting motion.
If you do decide to go with a tilt head, then I'd recommend Sirui L-10, which is without the panning base, and if you want to go with the panning base, then Sirui L-20S, which is what I use.
You have a fantastic lens and a camera. I wouldn't go cheap on their support system, be it a monopod or a tripod. I wasted a whole lot of money over the years by prioritizing "economical" solution ahead of expensive but quality solution. Now, I'm opposite because I figured out it's cheaper in the long run. I've recently completed what I think is my personal quest for the perfect monopod set up for birding and wildlife, and I cannot be happier: https://photography-on-the.net …read.php?t=1492670&page=2