Interest on Capital in absence of any clause in Partnership Deed

If the deed mentions or not, it is unfair towards other partner. But, since it is a startup, you can do what you have suggested. However, it looks like you need it written in the deed. 

https://www.taxadda.com/remuneration-and-interest-to-partners-section-40b/

https://www.charteredclub.com/section-40b/

Sorry, forgot to mention one important aspect, you will be given allowance and disallowance based on the criteria of registering under partnership act and making a deed. That is important because, it will impact net profits. This is some kind of company law I think.