Yes to lessons. Yes to theory. However playing with others will force you to get better. If a band is not in the picture, backing tracks or videos of the music you like ---- and play along to them can advance your skill level.
Yes, let Google find the chord progression for you and then play along using the bass line YOU COMPOSE. The root, third, fifth and seventh of the chord make a good bass line. Trick is to know how many of those notes to put into your bass line. Roots first, that takes care of Praise music, then the 5th, that takes care of Country and a lot of Rock, then the octave and the correct 3 and 7 fill out your bass line very well. The ole R-5-8-5 will play a lot of bass and as it is kinda generic - most all chords have a root and a 5th - so it will fit over most major and minor chords.
Theory - bits and pieces from Internet forums are just that, bits and pieces of the story. Get a theory book. Billy Greens' book that we normally recommend has some problems down loading. Perhaps the guys can give you a better address. If not I recommend Alfred's piano theory book. Theory is theory and works for any instrument.