i'm thinking with mass-hull design i might be able to fit two constructor mods on it.
You won't be able to. You can only have 1 construction module per ship. Hard-coded that way.
Two things you can look into to increase your build speed.
1) Make a new construction ship that just has the module and engines. If you're not going WAY out of your way, there is no need for life support modules. That is doubly true once you get 1 of those star bases in place since they count as a base point for distance for life support. Having this stripped-down ship will lower it's price and thus speed up construction.
2) Make a ship with a small hull with a construction module on it and however many engines you can fit. Typically their price will be lower than a cargo hull and thus build time will be lower.
If you are planning to try and influence flip the opponent, definitely work on any tech that'll give you an influence bonus. The one will even open up more star base modules so that you can get up to a +100% influence boost via that star base.
In addition, if you are playing TA 1.96, feel free to have taken the Evil ethics choice from Xeno Ethics to build the Mind Control Center (often referred to just as "MCC"). If you're not running that expansion and version, it would be best to not go evil and get the MCC. Prior to a recent patch for TA the MCC actually made planets HARDER to influence flip, yet gave a +100 econ bonus across your empire.