No water coming through brand new faucet installation

Sorry, these thing are often more trouble than they are worth. Without naming names, even the best of the best have seal and valve issues over an unreasonably short period of time. While they are quick and easy to install compared to a plumbed in model, they eventually leak from somewhere, the faucet, the filter cover, or, like yours, the cut-over valve.
You can, keep spending money on replacements, have a dedicated filter plumbed in, or resort to bottled water, all of which run the cost of purified water up beyond the price of tap water.

some new faucets come with there on supply lines when you tighten one will twist at the top near the faucet look under the sink to see if this has happened. i've had it happen not long ago

There's a clog in the shut off, line to faucet, or in the faucet cartridge ... hook it up to a supply tube on another faucet, it connect to a garden hose to check if faucet is problem.
Water pressure problems on following link:
http://waterheatertimer.org/Low-water-pressure.html

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When you turned off the water to remove the old faucet did you have to turn off the water to the whole house or was there cut off valves going to the tub. Did you install cut off valves for the tub and forgot to turn them back on before trying the new faucet. What type of faucet did you install? Whats the make and model. Its possible something got caught/dropped in the pipe when you were installing the new faucet and is now blocking the flow of water.

When a tankless is installed, they are usually set up with a recirc. Theis keeps the water continuously heating to some degree.
When a tankless is installed into a home it has nothing to heat the water that is sitting in the pipe from its faucet to its heat source. Now as soon as you turn on the faucet, you have to let all that cold water run out until the newly heated water comes out from when you started the faucet.
You could measure the volume until heat and it will be pretty much the same every time for a given faucet.

The fact that your faucets are low flo is only part of the factor involving time it takes to get hot water. Another factor is volume. The diameter of your pipes makes a difference. You can remove the low flo restrictor from the faucet farthest away to speed up the process at least a little.

check the tub faucet the pull lever maybe slightly faulty causing back pressure in line and pushing water up to shower head --u may have debris in tub line causing partial blockage -or u have alot of water pressure coming in and it is to much for the lines to handle and it is pushing up to shower head

SOUNDS LIKE THE CARTRIDGE ASSEMBLY IS BUGGERED UP. PART #46463.
MAYBE THIS WILL HELP:
All parts and finishes of the Delta faucet are warranted to the original consumer purchaser to be free from defects in material and workmanship for as long as the original consumer purchaser owns their home. Delta recommends using a professional plumber for all installation and repair.
Delta will replace, FREE OF CHARGE, during the warranty period, any part or finish that proves defective in material and/or workmanship under normal installation, use and service.
Replacement parts may be obtained by calling 1‑800‑345‑DELTA (3358) or by writing:
Delta Faucet Company Product Service 55 E. 111th StreetIndianapolis, IN 46280

when you installed did any teflon tape or debris get inside? you can remove and reverse flush with hose and it may clear the blockage

you may have installed the stem incorrectly or something is blocking the water passages inside

it's the thermostatic valvle to be regulated