Dutch is not as stable as other languages over time. We've had a few spelling reforms and trying to read 17th century Dutch is actually not that easy even for native speakers. Old Dutch is more similar to German than modern Dutch.
I live in Germany and I always joke that Dutch is basically simplified German. The two languages are obviously related but we got a bit pragmatic about some of their more convoluted grammar choices and they gradually disappeared from the language. For example, we have male and female words but we only use two instead of three articles: de for male/female, het for the neutral form instead of die/der/das. Which is similar to the English the and it. Several articles still used in German (e.g. des and den) completely disappeared from the language but used to be common. A nice example where you still see this are place names like Den Haag or s'Gravenhage, which is short for Des Gravenhage and refers to the same city (The Hague).
As for accents, those would be one of the things that got removed from the language or have become optional. E.g. you don't see a lot of ë used in modern Dutch anymore but that is a recent change (in the nineties). The use of computers has accelerated this because we use keyboards without support for this (English layout basically). In highschool, I used things like wordperfect and memorized some of the key codes for accents so I could type this letter. Oddly, an e with an umlaut is not a thing in German or in French.
Also as you mention we use letter combinations for things that have e.g. an umlaut in German. For example ö is written "eu" in Dutch. The ü becomes "uu" and we use oe for the German u. French accents used to be common but have not survived language reforms. We even have some 3 and 4 letter combinations that tend to confuse the hell out of foreigners. E.g. the Dutch translation of lion would be leeuw. Löwe in German would be close in pronounciation.
I lived in Sweden for a while. The Scandinavians did a similar modernization and simplification of their grammar last century. This actually makes it relatively easy to learn. It's a pretty regular language with a fairly straightforward grammar. Also, the grammars of Norwegian, Danish, and Swedish are basically the same. The Swedish use a few different letters e.g. ö in Swedish vs. ø in Norwegian and Danish. But otherwise the languages are very similar in written form. Icelandic is a bit weirder but basically a Scandinavian language as well.