I've had a similar experience, though thankfully DH is more down to earth than you and there's a strain of tightness which runs through the family, although it applies to very specific things.
I'm from a standard middly-middle class background, DH is from old money (manor house, multiple holiday houses etc), objectively rich but not super-rich oil baron types. Luckily DH has a well paid professional job and I'm reasonably paid, he also loves a nice excel spreadsheet, so a bit easier to deal with than your partner.
- Alcohol content - I don't think this is unusual in these types of families, and doesn't imply an alcohol dependency issue. In-laws always have multiple different wines for a meal (lunch and dinner), and buy cases and cases of champagne every year, drinking it on the slightest pretext, daily at times. They don't drink to excess though, I've never seen anyone tipsy/drunk outside student parties or, possibly, a wedding. Pre-children we were probably similar, but we don't drink regularly now, though we do have a lot of champagne cases.
- Clothes -
Your problem here is at least in part his refusal to put things away. I do know DH's cousins like this, they're just accustomed to it, thankfully DH's mother had more sense and brought them up to be more self-sufficient. I know grown adults who, when they go home, their old nanny (still living there) still sugars their cereal at breakfast and stirs it for them! If you can agree how much to save monthly (and make sure you can see he
is) then he should be able to do what he wants with his spending money. He might soon realise that buying new socks means cutting back on his lunches, and cut his cloth accordingly.
Luckily my DH wears clothes until threadbare, and is tight on some purchases but then splurges on some things and spends a lot on his hobbies. I have never unravelled the secret rules of what they are all tight about, and what is ok. DH has certain expectations of standards of basic living, but is aware enough of money to be horrified by the cost of achieving those things, so tends to be very tight on those things, whilst spending happily on luxury items.
- Wedding -
We had a similar issue., I really wanted a small wedding. We let his parents pay for most of it, and it was large and at the higher end of costs. A certain type of wedding is 'expected' and it was important to the in-laws to reciprocate the many invitations they receive. A small discreet wedding would have signalled a relationship that wasn't approved of/wanted to hide, and as I was not known in his circles, the signal it sent out was important. Apparently.
However, in-laws are pretty tactful, and so the day's details were left up to us. They controlled the lion's share of the invitations, and family expectation controlled some aspects of the day, but we were able to mix it up a bit. Are there any issues in your case re: showing his circles it's a proper marriage/reciprocation given you are not what they were expecting? How controlling are they generally? If you think they're going to be controlling every detail - dress, menu, venue etc giving you little say, then you'd be wise to go for the smaller one, and perhaps they could host a larger party for their own crowd? We did the latter as there just wasn't space for all the people they needed to invite.
His family's attitude to you does sound problematic; I'm sure I'm not what my in-laws expected but they're managing and are lovely to me. Firstly I'd make sure, crass though it is, that they know you earn more. Then tell them frankly if he wants that lifestyle, he's going to have to change career to get it. What are his 'expectations' (trust funds, inheritance etc)? If they're likely to be helping you with large deposits for house, school fees and uni etc, then that does mean your salaries go a lot lot further, so if that's the case, his lifestyle might be ok in the long run. Make sure you protect yourself though, make sure you've always got enough to get out if need be. Would there be a pre-nup?
- Lunch - He sounds a bit boring if his idea of the high life is an M&S sandwich, I was expecting lunches at the Ivy! But I get your point. I think the personal spending allowance monthly, after savings set aside, might help you here. DH used to dry clean his bloody sheets, but I soon stopped that.
- Gifts - I don't have to deal with that, as in-laws are pretty low key (aside from certain absolutely necessary expenditures such as yachts, skis, champagne etc). Maybe you could sell them and make some extra income that way? His attitude to gifts from you is a greater issue.
Some of this behaviour is normal for the upbringing, and might anyway adjust over time, especially if his personal spending money is restricted and he has to make it go further. His attitudes may shift over time as my DH's have. Sometimes he just needs things explaining. My DH does sound more open to reason than yours (though if we had a more limited income I'm sure he'd be kicking up a fuss about the lack of ski holidays, less than top quality food etc). DH is hilariously tight about paying for hotels, because 'surely we know someone with a holiday house there'.
I think the main thing to establish is whether his parents are likely to bankroll not just your wedding but also school fees, house etc. Then decide whether they're likely to interfere and whether that's important or not. Then figure out whether, with those costs potentially covered, you could loosen the purse strings a little.
I don't know how much was helpful there, but I do know the weird puzzlement about how such families prioritise their spending, and seem cut off from reality. If my DH had been exactly like yours, not appreciating gifts, not even trying to understanding expenditure/income etc, then I'd have had concerns about marrying him.