it's the standard way flush transitions are addressed in new tile and hardwood isntallations without placing other products under the tile to create a ramp that may or may not sacrifice the stability of the installation in the future. it depends on the thickness of the tile itself. what do you consider "quite a bit" ? also it needs to be asked, do you really want a ramp under your tile ? if you have a 1/4" tile with a setting bed made from a 1/4" notched trowel, the total thickness comes in just below a half inch. Using a 3/8" notched trowel increases that by 1/8" Using a 1/2" notched trowel increased that by 1/4" Plus with thinset you can squeeze the tiles down and butter them up alot more effectively to achieve the flush transition. this doesnt necessarily have to be accomplished throughout the entire install. It could be spread accross the last few rows to accomplish the flush transition. Mortar sticks to mortar alot better than any 3rd prty ramping product. This is the way flush transitions are supposed to be accomplished in tile isntalls.

Laminate reducers generally attach to the subfloor and lay over, but not on, the laminate itself. You need something that will butt into the 3/4" wood and overlap the laminate. My preference would be to undercut/rabbet a reducer using a table saw or a router table. Let's say the laminate is 3/8" thick. Set the table saw so the blade sticks up 3/8". Look at the 3/4" reducer and determine how far back you want the undercut to go and set the saw guide accordingly. Run the reducer through the saw repeatedly, with the 3/4" side toward the guide, moving the guide further from the blade after each pass. Once you end up with what looks something like a bit of an L, sand or cut the sharp edge that will overlap the laminate and put some finish on it. Install it at the laminate edge then cut your wood pieces to it tight as you install the floor. Another way to achieve the same thing would be to make a 3/4" wide thin cardboard template. Draw the profile of your stock reducer on the cardboard then cut it out using scissors. Trim it to look like the L I described but with a slight flat spot on the edge that will overlap the laminate and see how it fits. Using the table saw, cut the edge that will overlap the laminate, set the saw and cut the horizontal cut with the reducer standing vertically, flat edge against the saw guide, laminate edge side down, then make the one vertical cut with the reducer oriented horizontally, 3/4" thick edge against the saw guide. You can always practice on a scrap to make sure you won't ruin your reducer. Respect you table saw!. It can take a chunk out of you or toss something back at you if you get it crooked or try to force it. Basically what you're trying to make is a T mold that is only undercut on one side and butts up to the 3/4" thick floor. Sort of like this: http://ecx.images-amazon.com/images/I/41YHKQYNC4L._AA300_.jpg Of course this one would be flipped over so the recess would overlap the laminate.

More plywood is always better, but you need both a plywood underlayment "and" a CBU for the tile to "bond" to. We'll assume the OSB is a T&G and the joists are not over-spanned. I would refasten the OSB and make sure it is all pretty flat, then install either a 3/8 or 1/2 BC grade plywood underlayment over top. Run the underlayment the same direction as the subfloor, but keep all seams offset by at least a foot or more. Leave an 1/8" gap all 4 sides and screw it down every 6-8" sides and field. Don't worry about hitting any floor joist when installing underlayment. And do not use any glue for this when tile is the finished floor. Then put down a wet-bed of thinset and install the 1/4" Hardibacker. Leave an 1/8" gap here too and, again, do not try to hit any joist. Space the screws like the directions tell you. After it is down you must tape over the seams with CBU tape. Instead of a CBU you can use Ditra to keep the height down.

OK...the solid hardwood is factory finished. That's fine. It means that you can choose a solid factory finish so that EVENTUALLY you can get all of this refinished at the same time AND STILL end up with the same floor throughout. What you do is find the SPECIES of the hardwood and the width (and the thickness)...and if you can find the same grade/cut. Sure you can run it perpendicular to the hallway...so long as you are NOT on wood joists. If you have wooden subfloors the direction of the joists will dictate the direction of install. Regardless. So long as you get the same species in solid, you can always sand/refinish everything at once = same floor throughout the home. You do not have to do it today...but it gives you the BEST option to do it later if you want...or just before you put the house up for sale.