You forgot the biggest expense and the one that is impossible to “skimp” on: day school!
Regarding the others: you make many valid points. Here are some suggestions:
Food
Unless you want fancy china, which is really unnecessary, at most you need three sets of dishes– milchig, fleishig, and Pesachdik. Weekday/shabbos is not a necessity, particularly since many families a) use paper during the week anyway or b) generally eat milchig during the week and fleishig on shabbos. If neither of these applies to you and you want to make a weekday/shabbos distinction with table settings in addition to food, you can get a few nice serving platters or a crystal pitcher. No need for an entire set of new dishes. For Pesach, you can again use paper, but if you’d rather not do that, get a cheap set of Corelle (my husband and I brought a set of Corelle to Vegas because it’s just for the summer; kal v’chomer Pesach which is only one week). Corelle also stores well and doesn’t break (great for little kids who like to “help”).
As far as Pesach food, yes you need to buy all new stuff, but anything nonperishable CAN BE REUSED year to year if you store it properly and have the space. This is a huge money saver. Also, if you stockpile nonperishable Pesach food, you will have access to a wider variety of spices. It’s so annoying to only buy a handful of spices because it’s “only for Pesach” and then integrate them into your chametz stock, and really how many jars of cinnamon and garlic powder does a person need? Just be very careful when you are putting them away so that the lids close tightly and make sure your family knows not to touch it year round. Ideally, it should be stored somewhere that’s out of the way so no one will accidentally contaminate it. Also keep in mind in terms of stockpiling food that the grocery stores will run a huge sale on Pesach products the day after Pesach ends. Buy everything half price and put it away for next year. You must be careful though if you have already changed over your kitchen that you put it away IMMEDIATELY and do not let it get contaminated.
Regarding desserts, Pesach desserts are so not worth the money and/or effort anyway. Just serve fresh fruit, Elite chocolate bars, marshmallow twists/fruit jells if you like that stuff (I don’t, but many people go crazy over it), macaroons, etc. You can also make a KFP cheesecake with crushed almonds, macaroons, cereal, or cake meal for the crust, or chocolate pudding or chocolate mousse. Be creative. Pesach “cake” is disgusting.
Kosher food in general can get expensive, but it depends on how you eat and how you shop. Limiting meat and fish consumption is helpful, as is buying national brands that are kosher certified rather than frum brands (if you really want to support the frum brands, go ahead, but this will bulk up your grocery bill significantly).
Prepared kosher food is expensive, as are kosher restaurants, for a lesser quality than treif prepared and restaurant food (both my father and my husband were baalei teshuvah and could attest to this personally). Making food from scratch wherever possible will cut down on this cost. If time is a concern, cook in bulk and freeze things. Also avoid kosher frozen products, which can get SUPER expensive. It’s not worth the tradeoff in convenience.
Make friends with the reduced produce section and clearance shelf of your supermarket. You’ll have to plan meals accordingly so that the produce doesn’t spoil before you get a chance to use it, but it’s well worth the savings.
If you live near a co-op, join! Or get a Costco membership, or make friends with someone who has one and go with them.
Watch out for good deals on nonperishable food on Amazon (crazy, I know, but they have an extensive grocery selection which often runs really good deals). If you are willing to buy in bulk and buy when the sale is and keep it around until you need it, you will save a bundle. I have a case of almond milk sitting in my mother’s basement waiting until we settle down somewhere and can take it with us. I use almond milk a lot and got a REALLY good price on Amazon, and it’s shelf stable.
Find a blog or website that tracks sales and follow it. I like Kosher on a Budget. You can also just check the Amazon Gold Box page on a daily basis.
Just a few thoughts from a newlywed who’s starting to get a sense of how to run a household. Taking a break from the Internet now; will return shortly to post more.