I haven't played the CJ list for ages(I'm using Codex Eldar for my harlequins), but lets see what I can recall.
There is something weird in the CJ list, namely that harlequins don't get saves in hand to hand combat. This led me to play a pistol based list. I tried to maximize the shooting damage prior to assault and thus had both pistols in squads and one on the troupe leader (plus one on an eventual character, or a death jester's gun on a joined death jester. As far as I recall, a neuro-disruptor is fine too). This fits nicely in a venom, but is obviously an expensive and fragile target. On the other hand, this kind of setup should lower your chances of being decimated by a single tactical squad you charged and that never had the chance to shoot at you (Oh how many games I lost this way!).
Also, i believe that haywire grenades are mandatory. In fact, in the CJ list the harlequins do not have hit and run and thus being charged by a dread is your worst nightmare(he won't kill you, but you'll be stuck there forever). I fear that now that the BA have flying dreads of many kinds(librarian and transported), your superior mobility won't always save you. In that way, I preferred your original list. Plasma grenades are also a huge necessity, since you want to kill your enemy before he kills you.
Basically, when I played the CJ list, I tried to maximize the power loaded in every mean of transportation used. Essentially, every squad in your army, except the DJs, needs to be safely carried to the enemy. For that you have three options: the Shadowseer(0-1), venoms(0-3) and jetbikes. In my opinion, venoms should be as full as possible, to crush your enemy swiftly(both pistols, both weapons, troupe leader with stuff etc., perhaps a character(death jesters bear an extra power weapon, so when you don't need all the anti-tank firepower, you can throw one in too) ). The Shadowseer works nicely with a bigger squad on foot. Plus you can hide some jesters in it, for an invisible firebase that holds objectives. For mechanized duty, I preferred the Great Harlequin, because he is cheaper and better in combat. Jetbikes are a bit expensive, especially at 1000 points, but they have actual armor, and that shouldn't be overlooked.
I feel that a Solitaire is also too expensive at 1000 points. I'd allocate his points into more troops. You still need to grab objectives like anyone else.
Speaking of troops, i believe that CJ 44 added mimes to the list(I only used CJ 39 myself). In 5th ed, they might be useful as outflankers, giving you another mean of relatively safe transportation. Also, being reserve based, they are somewhat less vulnerable to deep-strikers.
I'm not sure about the spiritwalker, since it will be the only target of that type on the board and since your usual opponent should have more than enough guns to stop it, it might not be as useful as it seems. Still, I'd give it a try.
I however fear that the old CJ list isn't playable anymore. At all. Harlequins were slightly inferior in 3rd ed, weak in 4th ed and are downright masochistic under the new rules. If I was an IG player, I'd use one of those huge squads of conscripts/combined platoons and wait until you charge me. Then I would use the(relatively new) pile-in move that everyone has now and bring the fury of nearly 50 attacks upon your 6-7 guys(This could be a reason to use a dread mask. The misdirection power will also be quite handy). Using colonel Straken for his aura of counter-attack will make things even worse. Then there is guardsman Marbo and the instant demo-charge that negates your holo-suit save and appears from nowhere. Also, under 5th ed, Death jesters could as well be called free killpoints. (Unless I'm wrong, your last list has 10 killpoints on 20 models, including 18 with toughness 3 and a 4+ save and two paper thin vehicles. A Shadowseer with 10 footsloggers is probably the best way of avoiding the multiplication of kill points)