1. With Russia bowing out in Late 1915 with OTL Brest-Litovsk, would France concede to Germany some colonies? (French Indonesia or French Congo?)
Well, German colonial planners were really taken with the idea of Mittelafrika, that is, German Africa encompassing Cameroon, all of Congo and German East Africa. So, if they do ask, they'll probably push for Congo (as a foundation from which to work toward the Mittelafrika idea), rather than a region Germany has no reasonable way to project power to.
Exchange of colonies was a pretty normal thing in the period, so it's likely they'd change hands in the peace treaty.
2. Italy was never really discussed to an end point, and I'm still flip floppy on it. I was speaking with King Nazar via chat last night and we came up with the idea that Italy would join the Entente, leading to a trench/border war between Italy and A-H, but when the Russians bow out, the Germans in the east would swing South and plow through N. Italy. Is this plausible? If so, would A-H be able to get back Veneto? Would Italy then switch sides with the promise of French Tunisia and French Savoy and Nice?
Well, Italy joining the Entente is a possibility. As long as Britain remains neutral (Italy couldn't join any side other than the one with Britain in it), they could do it. They were cautious OTL, however. The Galizian disaster for Austria-Hungary, the failure of the Serbian offensives and the stalling of the German invasion of France all gave Italy the impression that the Central Powers were beatable in general and that Austria-Hungary would collapse with a good kick in particular.
Could political maneuvering force Italy into the war on the Entente side? Certainly. Their enmity with Austria was rather fierce and they had significant irredentist claims on the Austrian littoral (namely, all of it).
It pretty much would devolve into trench warfare, though. Maybe a repeat of the Isonzo offensives which didn't really do anything other than add to the lists of Italian dead.
OTL, the Caporetto offensive by the CPs (after Russia collapsed) was an overwhelming success, coming within a hair's breadth collapsing the Italian Army entirely and leaving the Po valley open. Now, OTL's forces were pretty much the limit as far as logistics were concerned, so more troops aren't the answer, but keeping the Italian Army from rallying as they did for, say, another day or so could turn the whole thing into a rout rather than a retreat.
Post-war, it's possible France tosses Italy to the wolves in exchange for leniency in the negotiations. In that case ... Italy is going to be in trouble. Depending on the Ottoman stance, they might lose Libya (to the Ottomans, though it's a near-certainly they'd lose the Dodecanese islands to Istanbul). Italian colonies aren't all that attractive, so they'd probably be left alone. Maybe reparations?
Now, regarding Veneto. Vienna has enough troubles at home and they know it, so I don't see Veneto being annexed. There would probably be minor border alterations (for a more defensive border) and Italy renouncing all claims on Austrian territory.
What follows is purely speculation, but hear me out: Veneto might be useful as a buffer for Austria and, thus, established as a separate nation (a Republic, to keep continuity with the Venetian Republic, maybe?). It could also double as a sort-of waiting area until Austria has brought it's own house into order, so that it can integrated into the Habsburg Empire with a minimum of fuss later on. It's fate would depend on the situation in Italy and Austria, however. Public support would be a problem, but if Italy winds up a mess (they did OTL and that's when they
won the war), the populace might rally to the government/idea of a Venetian Republic. Answering to Vienna might be a problem, but it's possible for the Republic to take on a life of it's own and wind up as a client/ally.