1) To reiterate, there is so much world to LOTRO that over-leveling is the rule, not the exception, and thus consumables aren't going to be needed before max level. Even at max level, they're basically like WoW Lich King flasks - required for raids, handy to have on hand for dungeons, but by no means necessary for daily wizard chores.
2) Professions are useful with raid / dungeon dropped recipes, but ignorable the rest of the time. But as you've already figured out, since you have to complete prior expansion tiers to level the current expansion tier, you may as well knock them out while you go. Then again, my main has always had Forestry and Mining, which gets you metal, wood, and hides for all my alts, with only a city alt needed for farming to complete all harvestable materials, so maxing out all tradeskills was little effort.
3) Allegiances had a ton of sidequests attached to them in Mordor, but Umbar's are just rep rewards with extra steps. The rest of the expansions didn't feature them. For Mordor, you'll get a wrapper quest that walks you through the steps once you progress far enough in Mordor. Umbar was clunkier, with them unlocking once you had done certain dailies enough times to complete a deed... but you can just hit your allegiance keybind (check your keybinds for what the default is) to start throwing items at it.
4) Sounds like you're in phase hell, where (for example) Minas TIrith has a pre-war, mid-Battle, post-war, and wedding phase. Fortunately they learned their lesson from that, and most phases from that point on were different zones with different geography... until Umbar reused Gondor again for a third of its landmass. (You can probably directly figure out when they historically had budget /staffing constraints just from the amount of terrain reuse.) That said, I didn't play many of those areas until I wasn't absurdly over-levelled for them, so I can't give you a level appropriate path.
