Once you have the spouse /settlement visa in the passport, how long can you wait before entering the UK on it?
Can you go in as a visitor before using the visa, even if you have the spouse visa?
How much money, at least, should you have in savings?
Every visa has two dates on it, 'valid from' and 'valid until'. So you can enter UK at any time between the two dates. Spouse visa is usually for 27 months, but since you can apply for settlement after 2 years, you don't want to delay your arrival too much or it starts to cut into the 3 months' leeway.
If you want to go to UK before the 'valid from' date, you can enter as a visitor (if you aren't a visa national, i.e. don't need a pre-obtained visitor visa), but you need to meet the requirements as a visitor - return or onward travel ticket, enough funds, and no intention to work. As for how much you ought to have, it depends where you are going to stay, how much travelling you do and so on. If you are staying with your spouse and they are paying for everything, you need a letter from them offering free accommodation and to meet all your costs. If you are paying eveything yourself, maybe £50 a day, more in London?