Yeah, that's correct.
A "major" or "minor" scale is mainly determined by the tonality of the third degree of the scale. So yes - a major scale with a sharp 4 is a Lydian scale, and a major scale with a flat seventh is a Mixolydian scale. (The nomenclature I used above isn't fully accurate in that regard - it does assume that you know the natural major and the natural minor, and defines the modes based on alterations to those core scales. The diminished can't really be done this way unless you specify all the note alterations. It's usually better to just spell out the entire scale.)
Ionian is natural major and Aeolian is natural minor.
Modes do have a lot of uses....but for the average bass case, they are mostly utilized as finger patterns. (You may be aware, but just like C major and A minor have the same notes, it's the same with all the modes - C major (Ionian) and D Dorian have the same notes, along with E Phrygian, F Lydian, etc. - they are all in the key of C, just starting on different notes.) You should know the modes inside and out, but recognize that most of the time, you'll simply be playing in key - so just use your ears. If you're playing jazz, you'll want to know how the modes can map to extended chords (but at that point you may be using altered or non-diatonic scales anyway).
Modes do have many uses in terms of reharmonizing a melody....but most people don't really do that anymore, so yeah. Just use your ears, learn the modes and the theory, and apply them to the fretboard.