Congrats on jumping into hosting games! You'll have a great time.
1. Miniatures
Think like a casting director, and sort your minis by role/type. Why? You'll very rarely have the *perfect* mini in inventory, and this system helps you find a suitable stand-in for your particular encounter.
Store your minis by the group in big plastic zip-lock bags (the kind with writable labels). They're easy to store, you can look inside them without opening them, and they're cheap.
I have a couple hundred WotC minis, and I sort them like so:
PC RACES (go through categories in order, putting the mini in whatever category first applies)
Monstrous PC races (Dragonborn and tieflings, currently)
Little guys (gnomes and halflings; can also be used for kids)
Cloth casters (human-ish; casters and scholars)
Dwarves
Elves
Archers (human-ish)
Melee guys in heavy armor (human-ish; can also be used for soldiers/guards)
Melee guys in light armor (human-ish; can also be used for thugs/bandits/townsfolk)
MONSTERS (again, go in order, and put the mini in the first category that applies. If you have a LOT of minis in a particular category, sub-divide by melee/ranged/caster)
Fleshy undead
Skeletal & insubstantial undead
Goblins & Hobgoblins
Bugbears, Gnolls, & other beastmen (including minotaurs)
Orcs & halforcs (and orc lookalikes: brutish armed Medium humanoids)
Animals (including things like hellhounds, displacer beasts, and owlbears)
Insectoids (including spiders & such)
Small monsters
Dragons
Things with Wings (Vrocks, gargoyles, harpies, sphinxes, etc.)
Humanoid extraplanars (azers, devils, archons, etc.)
Nonhumanoid extraplanars (elementals, etc.)
Large humanoid monsters (trolls, orgres, etc)
Abberations / oozes / weird monsters
Bigger-than-Large monsters
2. Dungeon Tiles
I don't use tiles; I use a grid. Still, it seems like you could group them by size. Organize them like paint chips: drill a hole in the corner of each tile, about 1" in. Thread a large, thin metal shower ring (something like
this) through the holes. Bam. Now when you need a 5x5 room or 2x8 hallway, you can grab the whole bunch and quickly sort through them.
3. Sounds like the ideal solution is something you can put up when needed, and store away when not needed. Folding card tables are your friends. They're cheap, easy to get into a condo, and won't get in the way. 34" x 34" tables are available for $35 at
Target.
Forget about a whiteboard top. Just buy a big Chessex mat instead. Ideally, buy two, so you can pre-prep two encounters. These things take wet-erase markers, and they get dirty after use--make sure no one leans their elbows on the table while wearing white shirts.

Also: don't use red wet-erase markers. They tend not to really erase.
That should do it. Start simple, start cheap. You can always upgrade your gear later, after you've a better idea of your needs.