Also is it worth it to assign more than one freighter to a trade route?
End of quote
Why not? If the planet you trade with is rather far away from origin, is rather developed and planet's owner is among those you want to trade with, you can establish all available routes with that planet. Remember: the longer way - the more trade income. But Take care of the routes being at war.
I usually have ~60% approval rating, so I increase or decrease taxations to keep this level, but I don't get more that 65% taxes(my convictions). And I keep morale level of planets more than ~60-80% building morale boosters in time and using other ways (see above).
If you colonize new planet at high level of game, don't worry if morale will be 1% or even 0%. Don't build mass morale boosters at that time. Just keep building usual buildings. Whwn you see that morale goes at level ~10-40%, build booster to make it >50-60%. I heard some people killing population of planet just to keep morale better... I don't act that ugly, it's not a foundations of good. But it's your own business.
Starbases are used for the following:
1. Giving bonuses to you/ally's ships (armor, speed, damage) and disadvantages to enemy's ones.
2. Mining resources (they give you some bonuses).
3. Giving your planets in this sector production bonus(to balance production of some sectors or to balance your income with your expences).
4. Increasing trade revenue.
5. Increasing your cultural influence in this sector.
6. Increase your range(so your ships may go further).
7. Make terror star (it can move slowly & destroy entire star systems).