I agree, Arabs are beautiful, I rode some in the actual desert once which was quite an experience!
As a first horse, there would definitely be question marks. It's not that there aren't sane, safe Arabs out there that make good amateurs horses, but I'd put them in the same bracket as other blood/sports horses and TBs in that they were bred to do a specific job and can tend towards flightly/spooky/strong/'hot' behaviour if not very well trained and kept in a routine that suits them - bit like working breed dogs when kept in pet homes really. On the plus side Arabs are probably the soundest/hardiest and long lived of all the 'blood' breeds, probably better suited to living out in an english winter and less likely to break than a WB or TB...
But then again, a bit like dogs, any horse has the potential to develop problematic behaviour if not properly managed, even breeds which are usually thought to be 'easier' have their issues, cobs and draught horses can be bolshy and bargy, welshes can be nappy and temperamental, connemaras can be strong and nervy etc etc. So if your heart is set on an Arab I wouldn't say it's totally out of the question.
Regardless of breed, for a first horse most people are well advised to buy an established horse that is already ridden by a competent amateur/novice and successfully doing the kinds of things you want to do, e.g. hacking. dressage, SJ. Avoid having to train a horse from scratch (i.e. by buying a youngster) or even worse, re-training a horse which has already developed problems with someone else or which has been a competition/professionally ridden animal and failed at that job, because in the latter case although it may be well behaved whilst professionally produced, the change of routine and leadership/handling in an amateur/novice home may upset them and cause them to push boundaries etc.
Your main problem if looking for an Arab or Arab cross specifically, is that their popularity as general/leisure riding horses has massively declined in the UK over the last 25 years so your 'pool' of potential horses to consider will be much much lower than if you wanted a different breed or weren't fussed on breed. For sports horses, warmbloods and irish horses are much much more popular, and those few breeders/producers/dealers who focus on the amateur riders market will mainly have native ponies/crosses, cobs and ISHs/crosses as this is what most people seem to want these days. I think if you go for an arab you will need to be really patient as one suitable for a first horse won't come onto the market every day, be prepared to travel to view lots of horses and rigourously say no to ones that aren't suitable, be prepared to consider an older horse (arabs do often stay sound and healthy well into their 20s so don't write off a teen), make lots of contacts with the arab showing scene and perhaps endurance as well?
Good luck!