Mainboards:
It is advisable to choose a model with PS/2 connectors for connecting a keyboard and mouse. It is advisable to have a DVD drive to install windows from optical disk (DVD-RW). But this is not necessary at all, it is possible to dispense with usb devices (mouse, keyboard, flashdrive), officially (100/200 series+ Z370, B365, H310C (H310R2.0)), by integrating the usb driver in the ways proposed by the manufacturers of the boards (fot example Asus EZ installer).
LGA1151: 100-series Chipset (H110, B150, Q150, H170, Q170, Z170) - full support windows 7
LGA1151: 200-series Chipset (B250, H270, Z270, Q270) - full support windows 7
LGA1151v2: 300-series Chipset (Z370, B365, H310C (H310 Rev2.0) ) - support windows 7 x64, have usb drivers. But does not have official INTEL VGA driver Intel UHD Graphics 630, a discrete graphics card is required with driver windows 7.
LGA1151v2: 300-series Chipset (H310, B360, H370, Z390) - official is not support windows 7, problems with USB drivers, and also INTEL VGA driver Intel UHD Graphics 630.
Processors:
LGA1151: 6-series (Skylake) i3-6xxx, i5-6xxx, i7-6700(k) - full support windows 7, with official driver for Intel HD Graphics 530.
LGA1151: 7-series (Kaby Lake) i3-7xxx, i5-7xxx, i7-7700(k) - support windows 7, with official driver for Intel HD Graphics 630. Minor difficulties installing updates for windows 7, but these are small things that are being solved.
LGA1151v2: 8, 9-series (Coffee Lake) i3-8xxx, i3-9xxx, i5-8xxx, i5-9xxx, i7-8xxx(k), i7-9xxx(k), i9-9900(k) - support windows 7 x64, subject to the choice of a mainboard (B365, Z370, H310C(H310R2.0)), but Intel UHD Graphics 630 official is not working, deciding to install a discrete graphics card with driver windows 7 (for example GTX 10-series).
Asus Mainboard: Z270-P, Z270-K, H270-Plus, H270-Pro, H270M-PLUS, B250-Plus, B250-Pro, B250M-Plus, B250M-A, Z270-A, B250M-K with Skylake processor: i5-6500, or i7-6700 (k), or Kaby Lake i5-7400, or i7-7700 (k). Make sure that the board has DDR4 memory.
The Z370, or B365 Mainboard would be a good choice, official support windows 7, with a discrete graphics card with support windows 7.
Asus Mainboard: Z370-P, Z370-A, B365-Plus, Z370M-PLUS, B365M-C, B365M-A, B365M-K with Coffee Lake processor: i3-8100, i3-9100, i5-8500, i5-9400, i7-8700 (k), i7-9700, i9-9900(for top ATX Mainboard).