My best recommendation if your not going to be having a new barrel blank installed is work with what you got. I do quite a few accuracy package jobs to Sendero's and can usually turn a 3/4" - 1" moa rifle into a 1/2' - 5/8" moa or better rifle with all the factory components. Here's what I would do for now and why.
Re-Crown - I typically set the crown back at least 1/8" of an inch into good rifling.
Lap Lugs - I check the head space prior to lapping. I rarely find an action / bolt that will not lap in and be out of SAAMI spec. If by chance it would fall out of spec I'll set the barrel back to pick up 0 head space. True the chamber may be a bit larger than a custom chamber but most Sendero's after tweaking can shoot pretty well.
Full Action Stress Free Bed - I'd recommend for know keeping the factory HS Precision stock and bed it. The bedding block if prepped correctly can be made to work as pillars.
If you break the factory barrel in properly you more than likely won't need to have the barrel lapped. Plus barrel lapping is a special process that only a rare few know how to do correctly. In a worse case scenario use the Tubb Final Finish. It sounds like it's not shooting terrible now so I really wouldn't mess with it unless it really takes a bad turn.
You can still order the stock you'd like since it takes about 6 months to get a McMillan stock in. Down the road when your ready to have a new barrel installed that is the time to have the action fully blueprinted, a Holland lug added and when everything is ready to go, pillar bed the barreled action.
You can't go wrong with upgrading to a Jewel trigger anytime.
Your bases, rings and scope sound fine.
All in all in my opinion it may be best to work with what you got until your ready to go with a new barrel then get everything done right at one time. No need to spend money twice.