What do you guys think? Suppose im playing against three casual players on a big map and i want to smoke them but want to defend my flank positions effectively and quickly enough with a star-base. Is that viable in this current game?
No; this is too expensive and will leave you unable to make the aggressive offensive moves you need to be making.
Your best approach is to purchase planetary HP upgrades to slow down enemies. They will be forced to buy lots of siege frigates (crippling their main army), advance deep into your territory and leave themselves vulnerable to ambush and counter-attack, or else wait a long time to bombard out your worlds. Tilt your forces accordingly to single out one specific opponent and try to overwhelm each one individually. Divide and conquer, and focus on maximizing your mobile fleet.
If im going to be attacking on one player with a big fleet then how can i defend myself more effectively than having to micro fleets.
You can't; if the enemies sync up their attacks and force you to defend on two flanks, you will not be able to attack unless you are very very good and are able to win even when grossly outnumbered.
how can starbase deployment be further improved to accommodate multi-front line defense and attacks?
Place your starbases aggressively to act as staging posts to help your offensive forces. If they're just to blunt incoming attacks, don't bother. You need to invest everything in military in this scenario.
Should they increase the speed to setup star-base installations for instant or give star-bases new abilities?
No; starbase upgrades come online quickly enough, and I see no reason to make them faster.