The Haynes manual is really not that bad, it's ok to get a general picture of things involved in certain jobs on the XJ. It was the first documentation I bought when I decided to get into doing things myself and had no idea about factory service manuals etc because I thought that was for techs only. It travels with me on long plane flights, mainly because it weighs almost nothing (and it makes excellent sleeping material)
Comparing a Haynes manual with FSM is useless.
In regards to following Haynes in repairs, the problem is, its not very specific and might leave you stranded halfway through a job. It is not year-specific most of the time, and since there are sometimes significant difference between production years, that can cause confusion. Therefore, a factory service manual for your year XJ is priceless to have (well, it literally is priceless since you can download one for free). The XJ FSM is a very nice read, which explains in good to understand terms everything step by step, tells you about how to test things, remove and replace them etc etc. Invaluable to have. If it even was for the fact that IF you decide to bring it to a shop, you can demonstrate you have done your homework, tell the mech what you have already tested and all and at least leave them the impression you know your ride and what you want them to do, reducing the risk of taking you for a ride so to speak, when it comes to trouble shooting and part(s) replacement. Nowadays, mechs tend to spend less time on decent diagnostic processes and lean towards the more convenient replacing parts until it works...and you pay the $$ if you have no idea about this or that, and will have to go with their 'expert opinion'.
See the dealer only as a last last resort. Did I say last enough? Insane pricing for Jeep parts is not uncommon (like my NSS which was quoted $1024 , yes the sensor, not the entire car around it, no typo, plus 2 months delivery time.....I ended up sourcing one from the US for $46 delivered 4 days after ordering which 4 years later still works fine).
Like was suggested: download a FSM and parts catalog. Read up on things you'd like to do, come here with any queries you may have. There is an abundance of knowledge provided by members, who can also tell you about the in's and out's of certain maintenance from experience.
When you have purchased a new to you vehicle, it is good to consider doing the "service" things yourself. So you know they're done as they should be. It may look daunting, but it really is not. I'm talking about renewing all your fluids, like oil/differential/transmission/brake/power steering and to do a so-called tune-up (new spark plugs, plugleads/rotor and cap. All these items can be done relatively cheap and no need for any specialised tools. It lets you start off 'fresh' and tune-ups for that matter are great preventative maintenance things to tick off the list.
I'm sure the feeling of doing those things yourself on the XJ will give a certain amount of joy, pride and feeling of achievement. I started off with only ever having changed a tyre on a car....but lack of money and the ever growing dislike of having to bring it to a shop and having to go with what I was told needed replacement, made me decide to start doing stuff myself on the XJ.
My first job I tackled was a waterpump...yes, it took me a weekend, FSM open next to me, forum at hand for "live" feedback.... but man I was happy when I got it done , knowing it had saved me a few 100 $$, because that what it had cost the previous owner when it was done...
Long story short: Go for it Martin, you'll be amazed what you'd be able to do with your XJ (and there will always be more).
