Questions 2 & 3 are well answered.
Re question 1: La Bodega and El Patio in Chapala both have open mics where you will meet musicians at all levels; from basic to pro (I would say most are on the basic side) And they mostly play older blues/rock (danceable music) and some country, right up your alley. My tastes, also after 50 years of playing, tend to go more mellow and there is an open mic at Buenos Ayres in Chapala on Fridays, geared to singer/songwriters. There is also a ukelele meetup. You shouldn't have any problems meeting other musicians.
Guadalajara doesn't have that great of a selection and prices can be quite high, especially when it comes to electronics. It's best to bring your own pedals. I searched in vain to buy a cheap, reasonably good guitar (like an Epiphone D100) because I didn't want to travel with any of my good guitars. Never found one and the POS I bought (a Campero), the tuners didn't work and I had to replace them.