Tourist extensions are normally done within one or two days.
Some immigrations only let you apply within the last week, although most accept 30 day prior to due time.
I suggest you just go and get handed over their requirements. Normally you’ll need your passport with copy of ID-site and last stamps, one pass photo, receipt of your TM.30 address registration if they’ll ask for it and 1900 baht in cash. You apply on a TM.7 form at the immigration and can just ask your hotel or landlord of a receipt of your TM.30.
You don’t have a multiple entries visa, but you can buy a re-entry permit at the immigration or at the airport before you at 1000 baht for single and 3800 baht for multiple.
You only report after 90 days consecutive days in Thailand, so no notification is needed and the “90 days clock” restarts when you re-enter.
Varies between immigrations, some allows you to apply within the last 45 days, most within the last 30 days, but some only within the last week. The extension will always be added to your last day anyway. You can apply where you are at date and your latest TM.30 address registration is registered.
Check with the Thai embassy in Stockholm, but the only actual visa who will cover your whole stay is a one year Non O-A visa. The requirements are minimum 50 years old, income minimum 20,500 sek a month, an approved health insurance covering min 100K USD, health certificate and a police check up.
This is rarely checked at the immigration, but you might risk that your airline will ask for it at check-in in Sweden as they’re responsible for that passengers fulfils formal requirements for entering Thailand. You could call your airline and ask for their policy regarding this, but the best and safest would be to plan and purchase the ticket before you leave. Personally I would not have gambled with this as you never know and some airlines are quite strict regarding this now, as you as an example see on Finnair’s website.
You can enter on a 60 days visa exemption and do a 30 days extension at your local immigration, leave and re-enter on another 60 days visa exemption.
Be aware that’s it’s a formal requirement for visa exemption that you’re able to show proof of an onward ticket within 60 days even though you plan to apply for an extension later. Also when you re-enter Thailand.
So if you use visa exemptions for this stay, the best might be to buy a ticket out of Thailand within 60 days before you leave. Spend a couple of days in a nearby country and re-enter on another visa exemption with your return ticket back to Europe.
If you want to cover your whole stay with a visa you could apply for a six months multiple entries tourist visa before you leave, but you’ll still need a trip out. The one year Non O-A visa could cover all your stay, but there are several requirements and you should be fine just using the visa exemptions here.