Learn English – How to use “verily”

The levels of formality are, in descending order: intentionally, deliberately, and on purpose. If you look at published books and journals that have blank pages, you'll find some with printed statements "This page intentionally left blank". That's because it's the most formal and the most neutral. Yes, deliberately is a synonym that means intentionally, but it more often has a negative connotation than intentionally does (especially among high school students, at least that was true when I was in high school), although both words are used both positively and negatively, e.g., That was {a deliberate / an intentional snub} (negative use, and Google Ngrams shows more frequent use of the former than the latter). Maybe that's merely because deliberately is more frequently used than intentionally is.

Wikipedia has an article on deliberate practice, however, which shows that word's very positive connotation. There are also Web pages for intentional practice that show its equally positive connotation. Google Ngrams shows that deliberate practice is more often used than intentional practice. On purpose is what children say for intentionally and deliberately, which is why it's the at the lowest level of formality of those three terms. They are not always interchangeable: register and context must be taken into account.

Modest and decent have overlapping semantic ranges. They can mean the same thing, but do not always. To further confuse things, they might get used in the same situation to highlight slightly different aspects of a thing.

Modest can mean behaving in a way that does not draw attention to oneself, of which clothed in such a way that it conforms with sexual norms is a specific case. It can also mean simple because simple things do not draw attention to themselves. From simple, the related meaning of not wealthy or not opulent emerges.

Decent can mean meeting expectations without having the connotation of exceeding them. It can also mean a morally good person, though not necessarily a heroic or saintly person.

Here we have the area where the two meanings overlap: they both imply good in a way that does not attract too much attention. But they are not always interchangeable.

So as to your sentences, I believe the average American reader would consider the sentences about the house to be more or less equivalent. The average American, though, would sense a slight difference in the sentences about the woman, because "decent" is a broader category than "modest". A woman might dress modestly, but lie, cheat, and gossip, none of her acquaintances would call her "decent".