[Nexus 7 (2013) Original Android Development] TheManii:
UPDATE: Do not use webviewgoogle, it cannot install properly and will cause FCs everywhere The config below has been updated to remove that line

Protip: If you're having issues installing gapps due to it saying you're running out of space, it's because you're using the default installer options.

v0.4 includes about 100mb of redundant apks and their associated data, it also starts with about 360mb free, so you have a total of about 460mb to work with. Preferably the rom should not be built with these apks included in the first place, as they are directly replaced by the google equivalents on the play store.

You can also use magisk if you want to avoid filling up the system partition, magisk and the magisk version of phh superuser works without issues on this rom. If you do use magisk, the amount of room you have is simply as much free space as you have in data.

OpenGapps: Advanced Features and Options

If you want to use opengapps, you should customize your install, this is the install settings I used:

(The below requires using the "super" or "stock" sized installers)

I only included the absolute minimum of apks to install, as the rest can simply be downloaded from the play store, note how it leaves me with ~200mb free still.

include
#--------includes--------
PackageInstallerGoogle
FaceDetect
FaceUnlock
Hotword
Search
GoogleNow
TagGoogle
ContactsGoogle
KeyboardGoogle
VRService
#--------removals--------
BasicDreams
Browser
CalculatorStock
CalendarStock
CameraStock
ClockStock
Email
ExchangeStock
Gallery
Launcher
LiveWallpapers
PhotoPhase
PhotoTable
PicoTTS
Provision
TagStock
#--------Force Removals--------
(Browser2)
(ExtShared)
(Music)
(OpenWnn)
# Manually remove:
# /system/lib/libwnndict.so
# /system/lib/libWnnEngDic.so
# /system/lib/libWnnJpnDic.so
(QuickSearchBox)

Here's the test report it generated:

# Begin Open GApps Install Log
------------------------------------------------------------------
ROM Android version | 7.0
ROM Build ID | aosp_flo-userdebug 7.0 NRD90M eng.pawel.20160828.204409 test-keys
ROM Version increment | eng.pawel.20160828.204409
ROM SDK version | 24
ROM/Recovery modversion | OmniROM-6.0.1-20160404-flo-HOMEMADE
Device Recovery | TWRP 3.0.2-0
Device Name | flo
Device Model | AOSP on Flo
Device Type | tablet
Device CPU | armeabi-v7a,armeabi
Installer Platform | arm
ROM Platform | arm
Display Density Used | 320
Install Type | Dirty[Data NOT Wiped]
Smart ART Pre-ODEX | false
Google Camera already installed | true
FaceUnlock Compatible | true
Google Camera Compatible | true
New Camera API Compatible | false
Current GApps Version | No GApps Installed
Google Camera version | Legacy
Installing GApps Zipfile | /sideload/package.zip
Installing GApps Version | 20160828
Installing GApps Type | stock
Config Type | include
Using gapps-config | /sdcard/Open-GApps/gapps-config.txt
Remove Stock/AOSP Browser | true[gapps-config]
Remove Stock/AOSP Camera | true[gapps-config]
Remove Stock/AOSP Email | true[gapps-config]
Remove Stock/AOSP Gallery | true[gapps-config]
Remove Stock/AOSP Launcher | true[gapps-config]
Remove Stock/AOSP MMS App | false[NO_Hangouts]
Remove Stock/AOSP Pico TTS | true[gapps-config]
Ignore Google Contacts | false
Ignore Google Dialer | true[NoRemove]
Ignore Google Keyboard | false
Ignore Google Package Installer | false
Ignore Google NFC Tag | false
Ignore Google WebView | false
Total System Size (KB) | 847656
Used System Space (KB) | 484172
Current Free Space (KB) | 363484
Post Install Free Space (KB) | 200620 << See Calculations Below
------------------------------------------------------------------
# End Open GApps Install Log

TEST INSTALL: This was only a simulated install. NO CHANGES WERE MADE TO YOUR
DEVICE. To complete the installation remove 'Test' from your gapps-config.

# Begin GApps Size Calculations
------------------------------------------------------------------
TYPE | DESCRIPTION | SIZE | TOTAL
| Current Free Space | 363484 | 363484
Remove | Existing GApps | + 0 | 363484
Remove | Obsolete Files | + 420 | 363904
Remove | basicdreams | + 44 | 363948
Remove | browser | + 0 | 363948
Remove | calculatorstock | + 392 | 364340
Remove | calendarstock | + 2228 | 366568
Remove | camerastock | + 4456 | 371024
Remove | clockstock | + 3640 | 374664
Remove | contactsstock | + 6056 | 380720
Remove | email | + 6220 | 386940
Remove | exchangestock | + 0 | 386940
Remove | gallery | + 5232 | 392172
Remove | keyboardstock | + 16924 | 409096
Remove | launcher | + 1564 | 410660
Remove | livewallpapers | + 0 | 410660
Remove | packageinstallerstock | + 4820 | 415480
Remove | photophase | + 0 | 415480
Remove | phototable | + 488 | 415968
Remove | picotts | + 6636 | 422604
Remove | provision | + 12 | 422616
Remove | tagstock | + 296 | 422912
Remove | webviewstock | + 44164 | 467076
Remove | OpenWnn* | + 1460 | 468536
Remove | QuickSearchBox* | + 396 | 468932
Install | Core | - 104736 | 364196
Install | contactsgoogle | - 7752 | 356444
Install | facedetect | - 608 | 355836
Install | faceunlock | - 10496 | 345340
Install | googlenow | - 14924 | 330416
Install | hotword | - 0 | 330416
Install | keyboardgoogle | - 22532 | 307884
Install | packageinstallergoogle | - 5004 | 302880
Install | search | - 44928 | 257952
Install | taggoogle | - 332 | 257620
Install | vrservice | - 3008 | 254612
Install | webviewgoogle | - 44776 | 209836
| Buffer Space | - 9216 | 200620
------------------------------------------------------------------
Post Install Free Space | 200620
------------------------------------------------------------------
* User Requested Removal

# End GApps Size Calculations

# Begin User's gapps-config
test
PackageInstallerGoogle
FaceDetect
FaceUnlock
Hotword
Search
GoogleNow
TagGoogle
ContactsGoogle
KeyboardGoogle
VRService
WebviewGoogle
BasicDreams
Browser
CalculatorStock
CalendarStock
CameraStock
ClockStock
Email
ExchangeStock
Gallery
Launcher
LiveWallpapers
PhotoPhase
PhotoTable
PicoTTS
Provision
TagStock
(OpenWnn)
(QuickSearchBox)

# End User's gapps-config