Cheers for the kind words Ste.
What club/level are you gunning for? My first piece of advice wouldn't be to worry too much about size if your playing at an amateur level. You look a decent size so hopefully at some point your strength should match that too! Pre-season will generally be endurance fitness/touch rugby for the first few weeks so don't worry about getting roughed up

Then training generally moves to more specific training, handling, skills, tackling, conditioning and other anaerobic work.
Most new guys (me included, I took up rugby quite late compared to most), concentrate too much on weight work, but some of the best players I know/play with barely touch weights at all, they're fast, skillful and fit. If you can outsprint your opposite man, you don't need to be 15/16st

. Also begin able to last the whole 80mins at a decent pace will make you a valuable asset depending on what level you play at. Again, you can be big and strong but if you knackered by 60mins, your pretty much screwed for the last 20, because you'll be hurting big time! If you can continue make the hard yards and pop up in support for the whole game, or have it in you to sprint at full tilt in the 75th minute when everyone else is knackered, you'll have an edge over others. I've played at my club for the 1st team, all the way to the 5th team, and I'd say the most notable diffeh difference, strength, a little difference, but fitness in the last 20/30mins seems to be what sets the teamsrence between the top 3 teams in the fitness. Size wise, not muc apart.
What position are you going for by the way? If you have an idea that is.
Obviously all clubs have their characters and personalities but I wouldn't worry too much about any pranks etc, not during pre-season anyway! Most clubs would be thankful for fresh faces and additional numbers so just enjoy it
If you have decent hand/eye co-ordination or play football, or other sports it should come abit easier. But all clubs welcome new players at any age, any level, just so long as they want to learn and listen. Again, depending on the club, you'll get a wide variety of people at pre-season. We generally get all the old Vets down who love the endurance stuff and put the younger lads to shame, but then tend to dirft off once the handling and skills bit start

so don't worry about being thrown into the deep end, give it a month and you'll find your place

. Plus, not all payers attend pre-season so think of it as a way to get to know other people and get a head start over others.
Sorry for rambling, hope it makes sense and helps!