no - you don't need to keep the joiny-in bits as one "style" (especially if you look at your traditional hymns that you use and you'll probably see that they range from mid 20th century right back to 1700's (or earlier 
).
Some of the "regulars" may suprise you. One of our staunchest traditionalists's (who argued "for" keeping our Evengsong service despite it being even"said" and only having about 6 people turn up to it) favourite hymn is "Be Still for the Presence of the Lord"
And yes I did tease him about that (despite him being twice my age) after he'd been complaining Loudly for weeks about all the new hymns/songs we'd learnt and then we had a praise service one evening where people could choose their favourite hymn and he chose "Be Still"
You could try some of the modern hymns that have been written to ease them in if you're really worried (In Christ Alone was instantly popular when we introduced that because of it's traditional hymn like format), and alsoones like Here is Love.
I also years ago compiled a list of popular (within the church) "modern" (post 1950's) hymns and songs that we already used in church and were included in our (hideous) Orange hymnbook. Sadly I've since lost it, but there were some looks of shock on faces of some when they realised just how "modern" some of their favourite "traditional" hymns were (Will you come and follow me was only written in 1987 for example).
And some of the "modern" ones which they disliked were written not long after the war
Stuart Townend is quite a good one to start off with. Very modern, but lots of his stuff in traditional format. Plus there are quite a few modern hymns around set to old tunes that they'll know well.
In principle many "traditionalist" are opposed to intrducing new stuff - but in practice few complain once it's intoduced and often embrace it better than some of the ones that like to think of themselves as more uptodate and contemporary.
One thing I would say is to choose your songs carefully, once they're used to singing some of the more contemporary choruses and songs learning new ones is easier, but initially (and especially if you're musician(s) are not used to it) some of them can be hard to grasps the rhythms (though in reality some are no harder than some of the older ones like A Great and Mighty Wonder - that always throws people in our church).
I second having instructions on where to stand/sit/kneel (if they want) in the service sheet. Some people will never have been in church before and if they have clear instructions in front of them then it makes it easier for them.
Digital media can be great, BUT make sure it's someone that knows what they're doing that sets it up. Digital media used badly/presented badly can be a real turn off.
Think of it like watching TV, if you watch a poor edited, badly narrated, badly shot documentary on TV you're not going to rave about it much, or probably not remember much of it. A well edited, well narrated, well shot one will leave a much better impression.
I think this is where many churches fail when introducing digital media into their services - you don't want to listen to someone stumbling their way through the reading, see the Vicar faffing around during the service, the people doing the collection dithering about what to do - it leaves and impression in your mind that isn't what you're supposed to have on your mind when you leave the church iykwim.
I suppose it's also a bit like a business meeting if you're using powerpoint (though to be honest if your church is going to be using the screen frequently it's probably easier to buy one of the many pieces of software that's available - makes life much easier and generally takes less time to prepare). A badly put together PP presentation isn't going to give a good impression.