Minecraft CurseForge

 I think you're referencing a Nether portal.

 Don't have to restart world. You may want to double check the mod pack page.

 Compressed skyblock (or whatever the name is) was removed, due to errors causing crashes and no development. It may be back soon, due to new development starting up shortly after it was removed from the pack.

 Refined iron is iron in the furnace. Can make a plate using your preferred method.

 I think official is on 2.5.4. I would hope with 2.6+ being the "final" version, they will be updating soon.

 Can get sugar from witches. I have stone spikes and an ender hopper (the one that takes a couple of obisidian, pearl, and hopper) and have collected one. I plan to use that one to make 8 vector plates. That will speed up my farm and hopefully get more sugar and other drops.

Edit: If you're struggling to move forward, keep in mind that iron is king of moving forward. Once you get it, you can move up to secundus dust and iron casings and such. That will start you towards having enough resources to not be starving for them. I'm sure higher tiers are even better, but iron seems to be the big turning point.