Choosing the right raise amount is a balance of two factors -- setting a number that is high enough to achieve your stated goals but reasonable or realistic enough to give you confidence in reaching your target.
Most campaigns that fall short of their goal fail because they ask for too much. Fundable rewards campaigns are "all or nothing" which means you need to meet or surpass your stated goal or you cannot collect any of your funds. Instead of trying to raise one round of capital to cover every conceivable cost, it's better to focus on just enough capital to reach your next major milestone.
Remember you can always raise more than your fundraising goal -- but if you raise even a dollar less than your goal you will be unable to collect any contributions.
Setting the appropriate timeframe is about giving yourself enough time to build up your campaign. There are very few campaigns that can be successfully completed in 30 days. The average campaign lasts 60 - 90 days.
Startups tend to be eager to collect funds, which leads to short fundraise terms, but it's important to give yourself enough time to build momentum around your campaign, a process which inherently takes a few months.
Your fundraise can last as long as you wish but an investor’s commitment will need to be renewed every 90 days until closing. If you don't successfully close your raise within that time frame, the investor will be given the opportunity to renew or withdraw their commitment (in case their funds are no longer available). This gives you the flexibility to take more time for your raise if needed. A typical equity fundraise is at least 60 days
Fundraising takes a lot of effort. It's not about just posting a profile and waiting for the money to roll in. Your fundraising goal should take into account how big your network is, how much time you can put into marketing your deal, and how much people will be willing to contribute for each reward.
Smaller, achievable goals, with plenty of time to execute, are always your best bet.