It's easy to DIY- though easier if you have a stand that will suspend the front! Personally, I wouldn't want to pay money to anyone to do this job, I did it myself for the first time back when I really had not much clue what I was doing and it went fine
It's just remove forks, unscrew tops, turn upside down, springs and oil fall out, put some new ones in, job jobbed. The hard part isn't doing the work, it's speccing the parts and oil.
At 10st though you don't want to go much heavier- I was about that weight when I ran that setup with Ohlins .8 springs and 15W Silkolene fork oil and it was too heavy for me, it felt great on braking and AWFUL on bumps, especially in winter. You're not far off the right weight for the standard springs, so maybe just a fork oil refresh will help you.
Preload adjusters IMO are a wee bit of a waste of cash in some ways, basically you're paying for simplicity. They do nothing you can't do with a bit of patience and effort, really- on the fly adjustability isn't all that useful unless you switch from 1-up to 2-up a lot or you intend to put on a lot of weight. But still, I got them and didn't regret it, sometimes it's worth paying for something you don't actually need.