1 a. There will be a difference. See this:
1 b. Investing a fixed sum regularly or dollar cost averaging is a tried and tested approach. You become less concerned with volatility. However, having a war chest ready to buy more when Mr. Market feels depressed is a good idea. Nibble most of the time and gobble sometimes.
2. I won't tell you what to do but I have given unit trusts a wide berth for many years.
3. See answer to 1a above.
I treat the CPF as a long term investment grade bond which pays an attractive coupon. Whether we believe in having an instrument like this in our portfolio will shape our decision to top up our CPF accounts or to put everything in the equities market.
Building a cornerstone in retirement funding.