1) Yes, I think the Great Harlequin should be given Leader.
Note, the addition of 'Leader' to Harlequin formations may be a bit overpowering in it's own right as it allows greater BM removal, although this would reflect the highly elite status of the Harlequins, even within Eldar circles. If it proves overpowering, we can simply change the name and associated condition to 'Commander', which would also more accurately reflect their leading other formations into battle.
2) Re-entry to the Webway would normally be accomplished by moving to a nearby gate. This could be through an activation, consolidation or withdrawal. Note, once in the Webway, BMs would remain and would need to be removed through rallying as usual. However on the loss of all Harlequin 'Leaders' (commanders) by turn 3-4, all the Harlequin formations would simply be removed from the game it being assumed that they have abandoned their 'allies' to their fate.
3) On portals, I was considering the use of Storm Serpents that can be destroyed rather than the purchased Wraithgate. Also, there are still some outstanding issues over the use of portals around blocking and activation etc that need to be reviewed elsewhere.
4) Yes I think the 1/3 allies constraint is too restrictive, and no longer necessary. For example, buying 2-3 Storm Serpents leaves very little room for any more 'normal' formations out of the 1000 points in a 3K army (and we are skewing the list towards that as a significant option).
The list now poses the Eldar player with conflicting choices around mobility, activations, end-game objectives and formation choices etc. which should provide a more challenging and flexible game for both players while still retaining the Harlequin 'look and feel'. While Harlequins are still likely to rip up opposing formations in assault, they must now be used with more consideration of victory conditions.
This does raise the question of whether the 'allies' 1/3 titan and airpower relates to the entire list total, or just to the portion assigned to the allies . . .
Also, I presume the 'allies' would still be allowed to bring on the Avatar near a Farseer . . .
5) I agree 1 Solitaire per list. The wording probably needs revising accordingly to be crystal clear. I also like the increased mobility to 20cm, very characterfull

6) I really like Venoms, the concept is sound overall and presents the ability to treat the 'pilot' and vehicle separately from the 'passenger'. However, the wording probably needs clearing up to explain how they would work; perhaps the following
Quote:
Notes: Harlequin, Holofield, Skimmer, Transport. (May transport one unit of the following: Harlequins, Mimes, Shadowseers, Solitaires, and Death Jesters). Units being transported are in the passenger seat, so may fire with their own ranged weapons and use their firefight value in an assault or to lend supporting fire. Passengers may be targeted by shooting or assault, but are covered by the Venom's Holofield
Given this represents the use of Daethdi fields etc I think the Venom ought to be 5+ RA (like the rest of the Harlequins this represents exquisite skills and speed etc). However, I agree that Holofield would make everything more powerfull and slightly more complex again, and would thus need
really carefull consideration.
Cost of the Venom is about right at 20-25 points considering the Wave Serpent at 50 points.
(I have never been a fan of the 65 point Falcon, though I guess we may just have to accept it here.) The point is that the upgrades of additional units and transport makes for some interesting sums; another reason to remove the 1/3 allies constraint which allows a little more flexibility (and choice) to creep in.