I wanted a tub for a second bath and bought a Kohler Elmbrook from HD, sight unseen. It's a fiberglass Kohler tub that is made for HD. We've been very happy with it for 6 years now. It's solid, retains heat, and the finish has held up. Insist that it is installed in a mortar bed.

That is great to know. Is there another way to install? I would like to appear somewhat knowledgeable when I request that.

I purchased a Kholer cast iron tub based on specs and reviews. It is great. Read reviews carefully and look at every spec and layout issue. Kholer has a good track record on tubs. Look on Ferguson website, which used to be Build.com

Is this only a tub or a shower/tub combo? This doesn't sound like a simple refresh to me. It sounds like a complete gut. Be sure to account for waterproofing the walls and making sure that the way the tub and and flooring come together is feasible with your current situation.

I have a Kohler showroom close to me - go to Kohler's website and look up locations.

While they only stock certain tubs, you can compare what one of their acrylic tubs looks/feels like to one of their enameled cast iron tubs (they have MANY acrylic alcove tubs - and only a few enameled cast iron ones). You can also see/touch many of their fixtures (shower heads/spouts/drains) - this way you can see what each type of available finish looks/feels like in person (polished chrome and nickel/matte black/brushed nickel and moderne brass).

I have a Kohler enameled cast iron tub in one of my guest bathrooms - I like how it looks/feels.

I also purchased my Kohler tub based upon specs and reviews as Kendrah and Seabornman (although I went to a showroom initially). I think many (most?) people do that these days.

*Regarding your question about mortar bases - most manufacturers highly recommend or require a mortar bed for acrylic bathtubs to provide solid, even support. Because acrylic is flexible, a mortar bed prevents the tub from flexing, squeaking, or cracking over time. Without a mortar bed, the tub's base might not sit perfectly flat, placing excessive stress on the plumbing.

There are some acrylic tubs that specifically are supposed to be installed without a mortar bed - however, most manufacturers either recommend or require one. I would have one unless I purchased a tub that has specs specifically instructing to not use one.

EDIT: I forgot about your tile question. You are overthinking it. Many people have 12" square tiles on their bathroom floors (pretty popular back in 90s and early 2000s) - and many different shaped tiles have been used on their tub/shower surrounds. Find tiles that you like and order samples + go to tile showrooms!

@dani_m08 Thank you for all the info and the reassurance on mixing tiles. I will definitely look for a showroom too.