Is it possible to have multiple characters on one Runescape account

No. All members start fresh at level 3 on Runescape '07. It's an entirely different game as far as the data is concerned.

Though think of the possibilities; a fresh start could be fun. Or it could be grindy. Depending on how you take it.

Note: This guide is for Oldschool RuneScape only, as RS3 has many differences in training for XP as well as huge distinctions from OSRS in weaponry and combat.

It's extremely difficult to determine the exact order in which to train these two skills as each level provides minor marginal benefits which change based on the weapon you're using. It may be up to you to decide which is more important to you in terms of accuracy or damage, but there are a few things to consider to help guide you in your combat routing:

• The amount of experience it takes to increase 7 levels in a skill is roughly the same as it takes to get to that level (starting from level 30 or so). So your experience at level 60 will be 273,742 and it will take 274,211 XP to get to 67. Therefore, a relatively balanced approach is best to keep marginal benefit/level high.
• Gaining levels in strength only increases XP/hour when your maximum hit increases, so it doesn't make sense to train strength unless you are planning on doing so until your max hit increases.
• Wielding a better weapon increases both your accuracy and maximum hit, so it is highly desirable to reach the next weapon type plateau if you are close in attack level.
• Note that changing weapon types will change how many strength levels you need to increase your max hit. This also applies to certain pieces of armor such as enchanted amulets and metal boots.
• I actually do suggest training defence, as it can decrease the amount of damage you take, thereby decrease the amount of food you need to consume while training and therefore decreasing the number of bank trips you have to take. It will also open up other options for increasing damage output such as metal boots and defenders.

Using these suggestions, I would say to increase your strength until your max hit rises. Then, use a max hit calculator to check how many levels it would take to increase it again. If this is past your next weapon plateau (so if you're using adamant, that would be 40), then train attack until you reach that plateau. Then switch weapons and repeat the process. I would also train defense so that it's less than 20 levels below your attack (so mith if you're using a rune weapon), but that's up to you.