anyone has drafted a term sheet before?

Nice. It will take a while but don't get too worried. You can get through this. Firstly, 20 pages seems really long. I don't think I've ever seen one over 10, and my fund did some VC rounds valued over $1B. Maybe the reason it's so long is because the startup has pre-drafted all the Reps & Warranties that will eventually be the Stock Purchase Agreement... IDK

Regardless, take a look at the NVCA's term sheet template: http://www.nvca.org/index.php?option=com_content&view=article&id=108&It…

Key things that you need to make sure you have right are: Purchase Price / Price per share -- This needs tie to your fully diluted cap table

Pre-money valuation (which + all money invested in this round should = Fully diluted post financing valuation on the Cap Table)

Dividends: Make sure you know what your firm wants these to be. Often they are 8% and simple interest but that is a fund by fund number and interest method

Liquidation preference: (Extremely Important) -- Are you -Non-Participating Preferred (sometimes called convertible preferred) which means you either get the value of your liquidation preference (=amt invested + accrued dividend assuming 1.0x liq pref) or the amount if you converted all preferred shares into common stock. -or Participating Preferred which means you get your liquidation preference + full participation when converted into common stock

Voting Rights: Check with your senior guys. How do you want to do this? Your firm may prefer a specific voting policy for board members. Or they may prefer a certain majority % of shareholders must vote to pass something.

Protective Provisions: The NVCA one is pretty comprehensive and most startup lawyers will try to strip out some of these. Essentially this is trying to say without the new investors authorization, you cant do these things. Generally the most important are: ii) amend, alter, or repeal any provision of the Certificate of Incorporation or Bylaws [in a manner adverse to the Series A Preferred];
(iii) create or authorize the creation of or issue any other security convertible into or exercisable for any equity security, having rights, preferences or privileges senior to or on parity with the Series A Preferred, or increase the authorized number of shares of Series A Preferred; (iv) purchase or redeem or pay any dividend on any capital stock prior to the Series A Preferred, [other than stock repurchased from former employees or consultants in connection with the cessation of their employment/services, at the lower of fair market value or cost;] [other than as approved by the Board, including the approval of [_____] Series A Director(s)]; vii) increase or decrease the size of the Board of Directors]

These provisions keeps your fund from getting diluted without your say. As well, they limit board numbers keeping your ability to control the board decisions constant

Anti-Dilution: You need to find out what your senior guys want to do here. This clause basically means if the next round of investment is at a lower valuation than this one, how will existing shares be treated so they don't get over-diluted. The math behind doing this on a cap table is messy but the most common way is to do the weighted average (exactly whats on the NVCA template)

Those are, in my opinion, the big ones. Regarding Reps and Warranties, that's a much bigger thing and I don't have a template to send your way. Let me know if that sections been heavily populated or not.

Hopefully that helps... Good Luck