If you have to remove 4 tiles to get to the valve, then you're removing far more of the surface waterproofing than I'm comfortable with. Especially if this was done with a modern vapor barrier in place or membrane. I'd MUCH prefer to go through the rear and affect the watertight integrity of the shower as little as possible. I don't know what brand of valve you picked, but pick the best quality that you can for this second go around.

I really like the California Faucets thermostatic valve i used recently - well built, separate controls for two outlets, both with higher than typical flow rate, and a large central temperature control lever or knob surrounded by embossed numbers for ðF styled as if it were a fine watch. They also have a huge selection of styles, finishes, and either round or rectangular bezels. I've also used one of the Hansgrohe thermostatic valves that used their universal box - also quite nice, though I think a chrome-plated plastic bezel is a bit cheap for something priced as an upscale item, and I'd like temperature markings (isn't that part of the point of having a thermostatic valve, knowing what temperture the water will be?) This one uses a single lever to control 2 outlets, but it still works well and incorporates water volume and a diverter into the same control, and yes it can send water to both outlets at the same time at any proportion. It's designed so the innards of the valve are all accessible from the front, and can easily be serviced or replaced without ripping out tiles or the back of the wall. The Kohler and Grohe thermo valves I used a few years back have both been discontinued, so not much point discussing them here (there were both good).

Just finished building my somewhat modest master bath addtion (I did all the plumbing myself). My experience deals with a stand up shower in this particular instance. After some resarch, I decided that I did not need to spend north of $2k on Kohler thermo valve, and I did not need 15+ GPM with 3/4" inlets. By the time I added the body sprays and a couple of shower heads i was in for over $3k which was way over budget. I ended up doing a Moen Vertical Spa. IIRC, I think it was about $1,300 with two shower heads, 4 body sprays, a handheld shower, 5 position diverter valve, and the thermo mixing valve. I just fired it up last week and am very happy with the whole set up. Moen does a nice job, they have some great info on their vertical spa and thermo valves on the moen.com website. It took me a full day to pipe, but I used long radius elbows and took my time to ensure good flow. Having both the pressure balanced and a thermo valve, I prefer the thermo valve and being able to adjust the flow volume. Plus I think it looks better. I ordered it online from faucet.com, no tax + free shipping....plus they price match. If you google the part number and you find a lower price and email it to the price match department and they re-quote the product. Customer service was superb and ended up ordering my sinks, faucets, med. cabinets, and towel/TP holders from them. Again, with no tax and free shipping the net result (to me) was a great deal. I go out of my way to keep from purchasing at the big box - but that might be my personal grudge, but they dont have anything "good" in shower valves in stock any ways, so why bother ordering it from them? Hope that helps.

I can’t answer your specific question, but we added a recirculating pump to our hot water system and it runs on a schedule...when it’s on, hot water is nearly immediate from any faucet/shower in the house.