looks tight to me for mulching. I would get the big wood out and mow the rest of the lot and it will look fantastic. With a mulching head, you will need to back up a lot as stuff gets kicked out/under the machine and that's especially true for round, hard wood. If you have a lot of experience with the head, you can minimize the ejection of material. If those big logs are rotted and you are set on mulching, cut them to a length narrower than your head and pile them in one location. Trying to chase logs or plane long logs takes a lot of time and you will still find them ejected under machine. Without much room to back up and maneuver, you will get frustrated.
If it was my job and I had a place for those big logs, I'd cut them to whatever length would fit in my dump trailer and then just get a rotary mower for the underbrush and as I stated, it will look fantastic. You won't have to back up as much and you can maneuver around trees. You will burn less fuel, too.
On some of the more rotted wood or "chunks", a little finesse with the rotary will chop it up enough to not be an issue.
Looks like you could really make those lots "pop" from the road.
"Life is tough, but it's tougher if you're stupid."