Soaryn is still working on XYcraft. He just hasn't had the chance to get a public release of his mod out. (I remember they had a 1.5 dev version on Forgecraft 2)
It's intended purpose was to replace chests and buildcraft transport pipes. IMO leaving liquids out makes perfect sense, but that's just me. Maybe something will be added sometime.
You could use an array of liquid transposers and ME interfaces. Just add crafting recipes for all the different buckets to the corresponding interface.
Would you rather use a version of Windows 7 on your PC that was labeled "build 34194", or "1.1.0"? Using a dev build could completely wreck your system/worlds.
Jenkins is sort of like GitHub. Not entirely sure myself, but I know that's where you get dev builds for IC2.
You create a modpack client which you upload to technicpack.net.
Each user then copies the URL into their browser and it downloads. It should be covered in Luke's guide.
Add mods to Minecraft by putting the files into the Mods folder.
If you like Redpower-style stuff look up Immibis RedLogic and Redstone in Motion.
If you really want IC2 you could add a dev build from the Jenkins. NOT recommended.
Oh, don't worry about block and Item ID's. If they conflict, just change them in the configuration files.
Also, your friend is wrong about Galacticraft, as Tekkit 1.1.5 runs on Minecraft 1.5.2 and obviously has Galacticraft.
There are a few tings you need to realize.
There are three official Tekkit packs.
(In chronological order) Tekkit Classic -> Tekkit Lite -> Tekkit
They all have their own pages.
Tekkit (the new one, called just plain ol "Tekkit") is the one you want. It has no IC2, but that is a positive aspect, because when even the buggy beta builds stop trickling out for IC2 you will still be able to update. Thousands of people are having a great time with the new stuff. Don't get stuck in the past.
Any mods should be compatible as long as they all use Forge and run on Minecraft 1.5.2 (which both Tekkit and Hexxit do)
Find out how to make your own modpack here.