Hello,
For branch devices you can check this link (check for Maximum number of virtual routers)
http://www.juniper.net/us/en/local/pdf/datasheets/1000281-en.pdf
There is no clear routing-instance limit for 1400 but we have maximum of security zones which is 256.
show log nsd_chk_only | match "Max Security Zones"
Max Security Zones = 256
Assuming you configure at least one zone per routing-instance, you will run out of zones before you run out of routing-instance limit so realistically, the routing-instance limit can be considered 256.
For SRX3000 series, you can check this link:
http://www.juniper.net/assets/cn/zh/local/pdf/datasheets/1000267-en.pdf
Regards,
Rushi