Definitely want to use senior docking clamps. Also make it more of a train with the engines at the front. You can also use Kerbal Attachment system as I think you can manually strut things in space with it.
Have to be the Komet Launcher, I am using it for my Small & Cheap playthrough, Rockets have to be under 150 parts and be as cheap as possible. It's also one of the few rockets I use that has SRBs on it.