You are making your journey very difficult, so unless you wish to visit Scotland, then you are at the wrong end of Britain
So fly to Scotland from Belfast, from ￡15 or Ferry http://www.stenaline.co.uk/routes/belfas...
Fly from Scotland to London, Eurostar to France
The easiest way is Dublin either ferry to Holyhead Wales or flight to London, across to Kent and over to France
Or Dublin or Belfast to Liverpool via overnight ferry, so sleep on the ferry and be ready get on with the day...Liverpool is great
ADD: Any driving/commuting you do do it in Ireland/Northern Ireland A1/NI so much easier/faster not Britain traffic and distance is horrendous.. so if you are going to Scotland, drive up to Belfast, not Dublin to Holyhead or Liverpool to Scotand
Take the Stena Line Ferry from Dublin to Holyhead North Wales and then the Virgin Train to London Euston. You should be able to get a combined boat/train ticket. From Belfast there are ferries to Liverpool in North west England from which the rail operator is Virgin Trains again. www.virgintrains.co.uk and Cairnryan Scotland with a not too frequent bus link from to Ayr Railway Station and the rest of Scotland www.scotrail.co.uk
www.nationalrail.co.uk The ferry company is www.stenaline.co.uk
Eurostar Trains operate from London St Pancras International to Lille and Parys Gard du Nord very frequently. London to Paris takes 2 hours 20 minutes. Fares from ￡69 return. Eurostar also do excellent rail/hotel packages. You can connect on to the French high speed network to reach other parts of France at Lille or Paris. For the lowest fares book well in advance. Booking opens 16 weeks ahead of your journey www.eurostar.com
The old Stranraer - Belfast ferry route was fine, with very good ship/rail connections. The ferry no longer goes to Stranraer but goes to Cairnryan which has no rail connection and means a connecting bus, so unless you particularly want to go via Scotland I would avoid it.
If you sail from Dublin to Holyhead, or go by Irish train to Rosslaire and ferry to Fishguard, you then have a convenient rail connection to London.
The simplest way from London to Paris is by Eurostar train but if you fancy going the old-fashioned way by rail and sea it is still possible, just not as easy as it used to be. See http://www.seat61.com/London-Paris-ferry... for possible ways.
(In response to your new addition): Going via Scotland does make more sense if you are coming into Belfast. Another adventurous route would be by rail from Belfast to Dublin (the UK's other international rail link, apart from the Channel tunnel) and as before sail to Holyhead thus passing through North Wales (possibly including a break there to see the mountains in Snowdonia).
Yes, Once you get to England just use the trains
Yes, whatever you do don't talk to strangers.
