Personally, I would do what you feel most comfortable with. If you know, honestly, that you will have the time to do the side jobs or know where you can quickly sell the whole rig for a decent price (offset the costs) then I would definitely pull the trigger on the rig. If you don't think you will have the time to sell or use the rig other places, I would just get the contractor to do it all and get it done RIGHT.
Not to say you couldn't do it right, but if you mess up or break something, it is all on you. Whereas if you paid the contractor and they break something or mess something up, THEY are liable for the damages (to your property or their own equipment).
Me personally, I would not pass up an opportunity to learn how to do all of this on my "custom" house. For an extra $5k, I would consider that money in knowledge transfer, well worth it.
BUT... to each his own.