You should inform your prospective new employer before they hire you. They have a right to know when the vacation will be and how long you will be gone for. If it is a particularly busy time of year, they may want to hire someone else.
Absolutely. If they get in touch with you before the vacation, just be transparent about the time you need off. It is very unlikely to be a deal-breaker if you're a good fit otherwise.
EVERYTHING in terms of compensation should always be spelled out in the offer letter, including salary, vacation, equity, vesting schedule, benefits, etc.
I want to confirm my acceptance of the position, with a start date of Start Date. I am excited about starting work and confirming the start date. I am grateful for the terms outlined in the offer letter and am confident that my skills and experience make me well-suited for the role.
The best way to tell your boss about a boss-requested vacation schedule is to take a written note to him or her to file away, privately, if necessary. With today's lack of security online, make sure you tell your boss in person with a note.
Be aware that in some situations, rather than offering a timeline themselves, they might respond by asking you how long you think you'll need. If that happens, one week is generally considered pretty normal. Ask for more than a week and you risk sounding like you're simply waiting to see if a better offer comes along.
I am very excited to join (Company Name) as (Your Job Title) and look forward to contributing to the team. I wanted to inform you that I have a pre-planned vacation from (start date) to (end date). I wanted to bring this to your attention as soon as possible to ensure that we can make any necessary arrangements.
Simply say I need a day to consider this offer. I will call you back tomorrow at X time to let you know my decision. Remember they are trying to fill a job and won't hold it for weeks on end. You will typically only have 1-2 days to accept the offer or they will give it to another candidate.
Just try and be direct and professional. Apologize, but not too much some. ``Unfortunately, I will no longer be able to accept the position offered to me. I understand that this is on short notice, however my circumstances have changed and I'll no longer be able to fill the role.